2009 Calabar border crossing & Cameroon Visa
It is still easy to get a visa in Calabar. You will need to provide a letter (in english) asking for a visa, a photocopy of your carnet and of course fill in their forms. Paid 30.000 west african cfa. I happen to have them from my last visit.
If you are doing the overland crossing, back track inland (north) and cross there. the road is actually shorter and is paved to close to the border. the 'direct route' is in terrible condition and is is three times longer than it looks on the map.
From the border to Mamfe, the road is its legendary terrible state and this way during the dry season.
As of 2009 they are rebuilding the road after Mamfe, so it is all dirt & mud after an initial 20 kms of asphalt. The old sections are often single lane in very bad condition. So expect this to be a problem for 2010 & 2011 at the very least.
I would recommend taking the ferry to Limbe or Douala as there are at least 3 sailings a week now. one is only 4 hours long.
I hope this helps you in your planning.
Suzuki V-Strom 650, KTM 640 Adventurer