Like Spuuky said, most of the complaints towards pre-3.0 phpBB versions were because they didn't really update it that much and holes were found a lot. It just got a stigma attached to it. I haven't heard anything major against phpBB3. I run it on my personal forums and really like it. It has a rich feature set, fairly easily modified skins, and is pretty modern in the overall design of the interface. I'd recommend it.