I googled around a bit for some more info on Maghrebi migration patterns and suchlike, and found this interesting document, which covers a lot of ground, including both historical patterns of Moroccan emigration to Europe and the newer phenomenon of Morocco as a transit point:

Initially, this flow from sub-Saharan Africa seemed to be a reaction to political turmoil and civil war affecting countries like the Democratic Republic of Congo, the Republic of the Congo, Sierra Leone, Liberia, and Côte d'Ivoire. Since 2000, however, migrants tend to come from an increasingly diverse array of origin countries. New origin countries of such transit migrants include Nigeria, Senegal, the Gambia, Liberia, Mali, Ghana, Burkina Faso, Niger, Sudan, the Central African Republic, and Cameroon.

Recently, even migrants from Asian countries, such as India, Pakistan, and Bangladesh, have transited through Morocco via the Saharan route. They are mostly flown in from Asia to West-African capitals. From there, they follow the common Saharan trail via Niger and Algeria to Morocco.

Although most migrants consider Morocco a country of transit, an increasing number of migrants who fail to enter Europe prefer to settle in Morocco on a more long-term basis rather than return to their more unstable and substantially poorer home countries. Probably several tens of thousands have settled in cities like Tangiers, Casablanca, and Rabat on a semi-permanent basis, where they sometimes find jobs in the informal service sector, petty trade, and construction. Others try to pursue studies in Morocco.

Yet sub-Saharan migrants face substantial xenophobia and aggressive Moroccan and particularly Spanish border authorities. Since most of them have no legal status, they are vulnerable to social and economic marginalization.

In September 2005, a Moroccan newspaper compared sub-Saharan African migrants to "black locusts" invading northern Morocco. Frequent round-ups have occurred in immigrant neighborhoods and in improvised ad-hoc camps close to the Spanish enclaves of Ceuta and Melilla and larger cities, and unauthorized migrants are regularly deported to the Algerian border.

...

Immigration control ranks high on the European Union's (EU) agenda, and, as a result, the EU's relationship with Morocco has endured considerable stress. In particular, the issue of Morocco readmitting undocumented migrants is a pressing but yet unresolved issue in negotiations with the EU.

Yet there is already a high level of bilateral cooperation with the some EU Member States, chiefly with Spain. Since 2004, Morocco and Spain have collaborated in joint naval patrols and readmission of Moroccan and non-Moroccan nationals in return for $390 million in aid.

...

In 2003, Morocco passed a new law regulating the entry and residence of foreigners. The law includes heavy sanctions against undocumented immigration and human smuggling but largely ignores migrants' rights. According to critics, in passing the new law Morocco is bowing to pressure from the EU, which wishes Morocco to play the role of Europe's "policeman" in North Africa.

...

Although the Moroccan government is formally complying with MEDA's and the EU's fight against illegal immigration, serious doubts remain about the credibility and effectiveness of these policies. First, on a yearly basis, MEDA aid is equal to only two percent of remittances. Second, besides a certain reluctance to play the role of Europe's policeman and massively expel sub-Saharan immigrants, which might also harm strategic political relations with sub-Saharan countries, Moroccan policymakers claim it is impossible to stop migration as long as the economic and political root causes persist.

Although the number of interceptions have dramatically increased in recent years, it is estimated that the majority of migrants reach Spain due to the professionalization of smuggling techniques and a diversification and expansion of migration strategies. Also, sub-Saharan immigrants who are deported to Algeria tend to return within a few days.

... (under "Future Prospects")

Although Moroccan policymakers and the media stress the temporary, transitory character of sub-Saharan migration, an increasing proportion of these officially "temporary" migrants might become permanent settlers. These African migrants to Morocco face substantial xenophobia and social and economic marginalization. At the same time, their presence confronts Moroccan society with an entirely new set of social and legal issues typical for immigration countries, issues that do not yet resonate with Morocco's self-image as an emigration country.

This also seemed interesting, though not directly related to the subsaharan African question:

Surging Remittances

In recent years, it has become easier, cheaper, and more attractive for Moroccans to remit money because of a government-encouraged expansion of Moroccan bank branches in Europe, the lifting of restrictions on foreign exchange, fiscal measures that favor migrants, and devaluations that increase the value of foreign currency. These measures are in line with the "positive attitude" adopted in the early 1990s.

At first glance, these policies seem to have reversed the stagnation in remittances. Since 2000, there has been a spectacular increase in official remittances, which stood at $3.6 billion in 2003. New labor migration flows to Spain and Italy and those countries' large-scale legalization programs in recent years also help explain the increase.

Morocco has been relatively successful in channeling remittances through official channels. Remittances are a crucial and relatively stable source of foreign exchange and have become vital in sustaining Morocco's balance of payments. In 2002, official remittances represented 6.4 percent of the gross national product (GNP), 22 percent of the total value of imports, and six times the total development aid paid to Morocco. They also exceed the value of direct foreign investments, which are also much more unstable.

The actual amount of remittances is estimated to be at least one-quarter to one-third higher — or about $1 billion — because money is also sent through informal channels or in the form of goods taken to Morocco.

Despite the level of remittances, few migrants seem inclined to start enterprises in Morocco. The Moroccan government, therefore, has tried to attract migrants' investments by offering fiscal incentives, reducing corruption, and removing bureaucratic obstacles to investment, such as easing administrative procedures for obtaining business permits.

There's also a Med-wide survey of migration that's worth a read.

Finally, and outside of the context of this link dump, from what I heard from some people working with migrants in Europe at a conference a couple weeks ago, Libya is now and has for a few years been making itself useful to Europe by accepting a large number of "transiting" African deportees without asking too many questions about whether they in fact had transited through Libya, and are in the process of building a number of large detention camps out in the desert near the Chadian border with Italian help.