As a Q&A site it beats phpbb hands down: much better search, wiki-like entries, rating of answers, simpler interface... It also has a fun side to it that I think encourages active participation. I'm looking at this forum's interface and it just reinforces the idea that they're on to something... The meta subsite would also serve the purpose of requesting new features, reporting bugs, etc.
There are also downsides, I'm sure, but I think the benefits would outweight them. Their success with Stack Overflow speaks louder than words.
In any case, their selection process seems to be quite strict and would require a more active community than the one we have now, and perhaps a larger one.
I can only say I've used Stack Overflow for a while and I've seen for myself that it works and I much prefer it to this clunky phpbb forum, but it isn't my place to decide anyway. This is like any other feature request. Some will like the idea and others won't. But I have the feeling, if the latter group tried SO for any length of time, they'd change their minds.