I've used the bus systems in two cities, Minneapolis and Reno. The system in Minneapolis is great if you need to get somewhere in the city. If you need to get somewhere in a suburb, be prepared to walk a few miles. Some bus routes, if I remember correctly (I haven't lived there since 2004), stop running at about 1AM and don't resume until 6 or so.
The system in Reno blows. The route that I used most often stopped running at 9PM, and to get pretty much anywhere, you have to take two buses: one to the central hub in downtown, then transfer to a second bus. There's a route in Minneapolis that conveniently goes through all the most popular places, through uptown and downtown and a district with lots of grocery stores, but there's no route like that in Reno.
I recently moved to Oklahoma City, and I suppose I'll become acquainted with the bus system here eventually, but I'm unemployed and living with my parents and rarely get out, so it's not a pressing concern right now.