Apparently KDN is offering free wi-fi in Nairobi (think it’s a promotion for their Butterfly product). It’s supposed to last through the end of the month. If you have a wi-fi enabled laptop, PDA etc. just search for the essid butterfly and connect. They are supposed to have around 100 access points in Nairobi.
EDIT: Riba and Bankelele, where did you try and connect?
EDIT 2: Article on the wi-fi offer.