All in all, I like it.
It generates valid html/css and has more administrative options than phpBB. Though in someways it does feel a bit more complicated to setup and use properly [keep in mind that *I have* been accustomed to using phpBB since 2003, and I did have to perform the extra steps of setting everything up and converting the old forum db to SMF].
On the plus side, it is much more secure than the nightmare called “phpBB”; though I do not like the fact you have to chmod 777 all the files — or at least some subset. Nor the fact that SMF does not seem to have as large of a community base as phpBB, which translates into “good luck finding the info you require, or locating a solution to a problem.”
The biggest hassle right now is with losing all the old URLs that have been indexed, that have good SE positions…
Indexed phpBB URLs are primarily of a post number while SMF uses a system where you have to start with a thread number and only then can you work to the post number. And since I have no way of knowing the thread number, all I can do is redirect back to index.php.
I’m going to stick to the default theme as it has a very clean and simple look. One other theme that I liked was called ‘DilberMC’, with the light silver color and an 800px width.
And just as a note to anyone interested in SMF, while it is free software, it is not GPL. The licensing termed specifically prohibit you from distributing the software in any way, modified or not. All generated copyright notices must also be retained.