I'll second that the Rules Compendium is a wonderfully useful book. I picked one up, and any time there's a rules dispute, it usually has a clear, concise answer. Granted, it's not perfect -- it's not indexed quite as well as it could be, and some things (grappling, ugh) are still just as poorly worded as they were in their original sources. Overall, though, it's worth the purchase for a group that ever has rules disputes.