Somebody may have already mentioned this, but there's a fantastic essay The Vietnam of Computer Science (2004) on this subject. It's long but so, so worth it.
Wow, thanks for contributing this to the thread. I had not seen this before. That has to be the best explanation of the tradeoffs/benefits of ORM I've seen anywhere. Most of the content isn't "new" in the sense that if you've done both a lot of SQL and a lot of ORM work, the issues are pretty obvious. But it does a fantastic job of showing why there's just no simple answer currently.
http://blogs.tedneward.com/2006/06/26/The+Vietnam+Of+Compute...