I think there are a number of these kind of sites now, but I found this one pretty quick and I liked that it had indexed the Bitcoin Mailing List archive as well as stuff from BitcoinTalk.

Here is an example of the results I got when I searched for "Satoshi Dice"

It probably isn't great at giving you a summary of things, but it might be useful for doing research. I'm certainly going to be experimenting with it a bit more.