I think such a service would be great. Last night in the middle of a very long coding session I got stuck on getting a particular SQL query working right for a couple of hours. I got a little help and some hints in #mysql on freenode, but I eventually needed to work it out myself. When I come across an issue like this that blocks progress on the project I'm working on, I'd love to have a service where I can drop some cash on getting help from an expert when I need to find a solution quickly.