Hi I have created a webmaster forum . Site Address - http://forums.1up.in You can join it if you find it interesting .
i think phpBB is not a great script for a big forum.i have problems when i try to copy the database and it has only 8000 messages in forum.
New skin maybe? For a webmaster forum, it doesn't seem to "webmasterish" with the default looking theme.
Few good advice are give above. I want to add one more. Try to blend the ad unit (at the top) with the background. Change the border and background colour of ad unit to white. Will improve the performance of unit.
When was the last time you heard ? the phpbb.com is now also using phpbb v3 beta5 . so its ofcourse much much stable .
Well , your forum is simple , you could add some elements to make more special , to create something different from the other forums. You can work at a header , a nice image on top would change the look of the forum. Also , I think that you can change the colors you are using. Add few more subforums and start promoting it , have some posts exchanges to get your forum rollin`
I agreed 'addlinkurl' idea, you may have problem when you want shift from it to other forum application.
Maybe hold off on the huge adsense banner on top until you get a bunch of loyal forum members, then slowly add some ads in. I did it with my forum and worked very well.