The background is a bit distracting but mostly because it makes it hard to read some of the things as you scroll down. If you could "dim" the background some by taking its translucency down to 60 or so % that might help.
The black background does limit the color of text you can effectively use, so maybe use a brighter text color or just change the black to a darkish grey.
All minor stuff in a very cool site!
I like the latest topics section as it provides info at a glance
and thanks for the warning on the ads...
Also like the ability to view posts the way you have it (since last log in, your own posts and those that are unanswered) very good idea!
I think this is great and am looking forward to some useful interaction!