Honestly, nobody seems to want to set it as 'Topic Solved'. Why? Either because they're lazy, or because they don't know how. Regardless, it's bad for business to have only a few marked as solved. It gives the impression that we get more questions than we could possibly answer, and that just isn't the case.
I think that if higher-posting members (maybe Devotees or something) should be able to mark as solved, you know? That way loyal members get a 'reward' (of sorts), and it cleans up the forum as well as lightening the administration burden.
I've admin'd a few tiny forums... and even if all of the users are following the rules, the upkeep is hard enough. I know that the phpfreaks administration could probably use all the help it can get.
Anyway, just my opinion.
P.S. My post count at this time is ~220. I just realized that it might look bad once I get the 500 posts, and I'm a devotee... and this post says that devotees should be able to do more. haha. 
Guru's+ (Guru, PFR, Mod, Admin) can all mark topics solved. The problem we run into, it can be really hard to tell if the OP thinks the topic was solved. Sure, sometimes its pretty obvious and they say "Hey thanks, that solved it!", but half the time when they have a working solution, they don't come back and post anything else or they'll present more problems.
Ehh, that's right, I suppose. :/
See, here was my idea (just for something fun to do):
Set a link in my sig that says something like "Click here if this answered your question"
When they click a link, it takes them to my script. My script grabs the referrer, takes out the topic ID, and shoots them back to the 'Topic Solved' page for that specific topic.
If they're the OP, it will solve. If not, it will make an error. One problem though: sesc.
The 'Topic Solved' page requires a $_GET['sesc'] to authenticate, and I don't know it for each user. I was thinking it might be something that I could clone (like a simple encryption of the user ID and the current time, or something), but I really don't know what it is. I started looking through code, and figured out that the forum is running this mod:
http://custom.simplemachines.org/mods/index.php?mod=1601But from there, I couldn't figure out $context['session_id'] (although one user said it was set by $_SESSION['rand_code']... which means it's stored server-side.
What a waste of time. :l
haha.