Ooh! Ooh! Me! Me!
But seriously, all of my work so far has come through these forums (this one and a couple other boards on similar subject matter). It's a good way to get in contact with people who have similar interests.
I haven't had any of these arrangements come through entirely yet, though. So I can't say for sure how trustworthy simply having an online community in common makes someone. I know it would have a powerful hold on me-- obviously, I've invested a lot of time and effort into my online identity, as I have the same username at four forums and have cumulatively posted well over a thousand posts over the course of a number of months, and I stand to gain a great deal if that online persona is seen as credible by the communities in question, and if I blow it and get a bad rep, then I've lost a huge investment of time and effort. So letting down a fellow member of that community would be a very poor move on my part.
However. We all know that not everyone takes these communities so seriously. I was involved today in a terribly stupid incident involving a spammer on the board where I moderate, and it's quite common (though, to give credit to the mods on these boards, I was never aware of it until I became one myself and saw all the hard work they do, among other things making sure the members have as little awareness of it as possible-- wow and

to all of them, because I never realized how hard they were working)-- people don't take the communities seriously and try to use them to spam.
So it's perfectly possible to be taken in, here as anywhere else.
So, like any other place, you have to use your judgement.
I don't know how to gauge whether someone's got a strong work ethic-- I mean, I post a lot, so obviously I'm somehow dedicated to this place, but is that because I've got a strong work ethic, or because my work ethic is poor and I think this is playing? (I'm trying to use mind control to get you all to choose the first option. Mmmm... Is it working? Hey, I'm typing this from home, and I could be taking a nap right now if I weren't so dedicated.

)
If I knew how to reliably find dedicated, creative people with fabulous work ethics, I would be a very highly paid head-hunter, and not some poor slob trying to make a buck as a writer. But, I think Deborah's right and the forums, with a few caveats, do make a good place for people with similar interests to connect. I want work, you want a worker, we can come to an agreement, etc. As long as nobody's spamming.

It seems the most effective way to go about things, to me. I'm also looking for work on other community message boards and job boards and the like (and I assume that would be another place to look for workers), but I prefer forums because it's a person you're talking to, not a number or an email address.
I can't speak as to the arrangements one would be better off making. I've certainly been pondering this. I thought briefly that I could put together a full-service webdesign company out of just my friends, but then I thought that would be too much hassle. Instead, if I get a job and the person needs general SEO, I have a buddy I can send them to whose rates are reasonable, and I know where he lives. I know a fabulous graphic designer who can always use a job or two, I know two or three excellent web-development programmers including the guy who did Kodak.com's DHTML UI and has an expensive fencing habit he's always looking for work to support, I know an absolute XML genius with some spare time.... etc., etc. You see how it sorta grows informally. Maybe someday I'd want to make that more official, but I'd rather start simple and see where it goes from there. And I can personally vouch for each of those people; if they don't follow through on a job, I won't send them more work, and I'll tell their mom, and they'll never hear the end of it.
I think the Internet is actually reinforcing interpersonal connections... but that's probably a rant for another time.