SMF is not that new - in fact it's an evolution of the popular YaBB SE forums (they chose a new name to avoid confusion, as there's a perl+flat-text forum software named YaBB which got a bad press for being resources-consuming, unstable and unsecure).
Here are the main reasons why I converted this board from phpBB to SMF:
- phpBB's database is overkill, since it builds a search index (to speed up searches) that will grow much bigger than the whole rest of the database (including the postings and everything else). Some may consider this word index a big plus, for me it's a waste of resources. I was afraid our host sf.net would complain sooner or later
- SMF is faster (building the pages)
- SMF's search is more user friendly, since "regular" user don't understand that they can use boolean operators in their search queries
- SMF has much more granular permissions management
- SMF has sub-boards
- Integration with Coppermine is easier
- phpBB will only highlight unread postings for as long as the session lasts. If you come back later, all postings will seem to have been read. SMF instead keeps track of what postings you actually have read in the db. This is especially helpfull for supporters who read all postings and try to keep track
- files can be attached to postings
I used to run several Yabb SE boards, so the SMF's admin concept came easier for me - it's a matter of taste as well; imo the whole administration concept of SMF is better when compared to phpbb.
Of course some will say that there are mods that will add some features to phpBB as well, but did you ever upgrade a modified forum? Can be hell, I wen't through this often enough. If you don't modify SMF's code, but only use the admin features that are there, you can have everything you need.
Another issue for me was the subSilver theme: I just got fed up with it - it's much easier to modify SMF themes to have a uniquely looking board (well, right now the coppermine board is still based on the default SMF theme, but this will change as well - I'll try to make it look Coppermine'ish asap
I didn't shy away from the fact that SMF is still beta because I know the guys from the SMF team: they're very modest and shy away from calling a software stable unless each and every tiny issue has been ironed out - I'm sure that SMF beta won't break that easily, and it has been tested a lot already - it's YaBB SE 2.0 after all, when you look closely...