Does the forum act as its own entity? Once you create a site design and want to add the forum module, can you just add the forum into a page so that it works with the rest of the site template, or does it have to be fully designed and templated on its own to match the rest of your site?
Jeff, further to Lindas answer…you don’t have to do any design work at all if you are happy with the themes it comes with - just click the button to activate the module and pick a theme…and you are off and running. It does not inherit any themes or css from the other parts of your site or EE.
In many case, the existing themes will do with some very simple changes - for instance, replacing the logo up in the top left - etc.
It’s pretty easy to hack around in the templates - much harder if you want true “design” work…...but since most forums are based on function over form, this is usually not a problem. Some…or even MOST of the popular forums on the web are pretty much “stock” as far as the styles go.
As an example, my forum has a new logo and some banners and links, etc…...see:
http://www.hearth.com/econtent/index.php/forums/
Nothing fantastic, but enough to slightly personalize it….