A great extension that's simple, easy to use, and integrates well with Joomla and themes.
Beware that they say on their website that the version for Joomla 2.5 is in beta mode and has been that way for quite awhile now. But, I decided to go for the beta version because I know enough of what I'm doing to fix things if needed. But no fixes were needed, it worked nearly flawlessly.
There is only a light and dark theme, which I didn't realize were the only themes, but they worked well with my website theme anyway. The "rounded" versions don't work on IE, but that's just because IE is so behind times with CSS standards.
The plugin is really easy to install, setup, manage, and it integrates with Joomla's core very well. I didn't have to modify much code, so I don't know how well it's written, but it seems to work well and beautifully integrated.
Overall a great simple forum if you're not looking for something with a lot of bells and whistles.
It also has great functionality for creating private forums, which was essential for me.