The exploit code is geared towards MS Internet Explorer, and if you're running Firefox, you'll probably just get locked up and not see any virus activity. Also, this may be one of the smarter scripts in that it only runs once per IP address... so if you never turn off your DSL/Cable Modem, you might only "see" it happen once.
This is NOT an occassional thing. The code is there. You can't see it using the standard "view source code" in your browser, but when you look at it using some of the debugging programs out there, it's there. It most likely isn't directly coded on the web page itself, but there's a script somewhere within the bulletin board suite of programs that is corrupted and is inserting the malicious code into every page.
The fact that I've emailed screenshots of all this to an admin, and just been told, more or less, "Yeah... we're going to redo the site anyway" leads me to believe nothing will be done about this. I understand the whole hobby website stuff - no one is making money on this even with banner ads, etc. But in my opinion, if you're going to have a website, you better be darn sure it's not spreading junk like this around to unknowing people. It's just not right.