OP (and Mods) I think this is an excellent idea. Perhaps the OP would volunteer to maintain a list in Post #1 of this thread. Might I suggest it be organized like this:

offerer; offer; unique terms; month/year

So, for example:

SPG Amex; 30,000 SPG pts; 10k/20k after $4500 spend; Aug 2011

This could be a useful resource (when it gets reasonably comprehensive) for evaluating the relative worth of a particular offer.