I think the two sites are complementary to linode/slicehost documentation. StackOverflow and ServerFault are not a general guide on how to setup a server from the ground up. I would only go there if I had a particular problem with my distribution or programming question.
I know, but I also believe it would be great if those two sites served as a hub for companies like SliceHost and Linode to put their support material, which could then be readily improved by the community.