Agreed, I always find it better to code things myself... I have the ability to make them more efficient, not to mention seamlessly snap into the site better as well...
I do list the platforms that have already built revenue sharing abilities (with the plugins/mods). See sig
Yes...it is very much "in" now a days. I have come across many forums and sites practicing this. So, nothing wrong in it!!! Relax and do it.
I am surprised too, maybe its because they have answered this question quite a few times they consider it common knowledge .... but I could not find anything in their HELP try reading through this thread http://forums.digitalpoint.com/showthread.php?t=519 Its from when shawn made his adsense sharing code (maybe it will help)