I'd be happy to put money towards the running of the site, but I would agree with some of the comments here.
when I first started using mediaportal the forums were really helpful in getting through some of the setup and asking for a fee to post questions would undoubtedly sare people off
How about a donation/pledge drive like Wikipedia have done? Cap the amount at a years running cost, people can then donate what they like.
As others have said, you don' want to scare people off. So a forum tax is not a great idea, simply because you want to increase your user base - not scare them into going with MythTV, Sage etc.
You can't charge for downloads (how does SourceForge survive...?)
Asking those who contribute to plugins etc. (and I speak as an interested party here) seems like a retrograde step and almost certain to halt contributions in their tracks (recent 1.01 delays for improvements come to mind)
I agree that $10 isn't a huge stack of money but it does beggar the question of how many people would bother once the system is running smoothly (and here I am thinking about the V2, I don't want to be caught in a permanent upgrade cycle so it would have to be HUGE to be worth the effort).
Maybe a >>suggested<< contribution on download, seems to work for some others. I have paid for CCleaner, ForTheRecord (and MediaPortal) amongst others because I found them useful.
Maybe streamlining the system is not such a bad idea - while it is a thankless task slimming down the forums would be well worth it for the ease of finding things!
I don't want MediaPortal to disappear but I would always be cagey about permanenetly paying for something I already own (why I gave up Sky+ in fact).
Is there nowhere that this can be hosted, even if you restrict the hours to evenings only - what are your office server(s) doing then?
Personally, I wouldn't mind paying the $10 a year to keep the forum, but I do agree with the comments that it might put off new users.
Is the MP site not busy enough to get much benefit from the Google ads then? A friend of mine is involved in a PS2 emulator site and he actually makes a profit from it AFAIK, mostly from the ads.
Also if you post current traffic information, maybe you will find donors as the server itself.
I am running my own commercial server, and I am sure there are several of us here.. Depending on the traffic required, you may be better getting donation this way?