I agree with Alex. I've been in Mali alone in november 2007, nothing planed in advance...
been in Segou, Djenne, Mopti, Dogon country and Tombouctou. also stayed in Y A PAS DE PROBLEME hotel in Mopti and in Sevare in Via-Via.
You can send me a PM an I'll give you the names and phone numbers of some guides.
But it's strange, I met a very few people traveling alone in Mali. I felt safe and had a great time.
In Tombouctou one family invited me for a lunch and it was incredible!
Go and enjoy, the Dogon country is something really special.