From a design perspective cool.
Hi Forbait,
Its pretty good, its been through alot of security tests to make sure its more secure than the previous version.
Unfortunately installing plugin's for it is quite difficult until they develop a mod-module for it.
If you have the coin I'd say Vbulletin is a good bet since its fairly well developed, if you don't mind spending some time ironing out the kinks PHPBB3 should be good.
From a designer point of view phpBB3 is excellent - especially compared with themeing in SMF and Vbulletin.
Joomla.org switched their forum to phpBB3 and it looks like its going to be bridged with Joomla as a forum solution - not sure about bridging though myself - Just something to consider as a site grows you may find you need content management.