Since I started Web-publishing, I have always heard that iframes are not a recommended solution for your Website: For some reason, they were evil, and the W3C was not approving its use as a “best practice”. I would hear that search engines crawlers hated it too.
Well, things might be changing up in here. First, a few weeks back, we could read on Inside Facebook that Facebook was actually moving away from FBML and closer to iframes. If the number one Website in the world starts to use iframes massively, I think we will all start to re-consider the W3C stand towards iframes.