KIAaze and I have been discussing just recently what collision detection iteam should use. We have came up with the thought that iteam should use only bounding-box for characters and moving stuff. It is faster, simpler and used more often than polygons. There is an interesting site, http://www.30daygame.com/ , where they are making a game in 30 days. They are using the bounding-box method and they are using two layers for terrain detection. Both of these ideas are simple and are known to work.
Now I will wait for opinions and hopefully a quick and painless decision.