ICG appears to be the only source that continues to monitor this situation in-depth:

Nigeria's Faltering Federal Experiment, dated 25 Oct 06

...Escalating violence, especially in the oil rich Niger Delta, threatens the integrity of the Nigerian state and raises the spectre of attempted coups by those who feel their privileges are being endangered. In the 46 years since Nigeria gained independence from Britain, successive governments have attempted, with varying degrees of sincerity and commitment, to fashion federal institutions that can accommodate the country’s ethnic, cultural, religious and linguistic diversity and nurture a sense of national unity. However, the leaders of these governments, at all levels, have failed to live up to their obligations to offer good governance based on equitable political
arrangements, transparent administrative practices and accountable public conduct. Communities throughout the country increasingly feel marginalised by and alienated from the Nigerian state...

...The government must address these core causes of the failing federal experiment or risk that Delta militias decapitate the oil industry, intercommunal violence spirals out of control, and ethnic militias, sectarian vigilantes and separatist groups continue to plague communities. Since such a destabilised Nigeria would be highly detrimental to the entire fragile West
African region, still struggling to recover from the wars in Liberia, Côte d'Ivoire, Sierra Leone and Guinea Bissau, the international community has many reasons to encourage far-reaching reforms.