It's kind of a dead site in a lot of ways, but there is a core group of really cool people there (some in relationships who met through the site). Lots of them just login for their forums, where there are some pretty interesting discussions. I don't really bother with it too much for the matchmaking because there aren't many guys that interest me in my area (yeah, in NYC where we have over 8 million people). I definitely would not pay for it, so I just have the free membership.
I have connected with two guys for LDRs there. One of them went nowhere, but I'm still talking with the other. I'm not sure when we'll meet. But I actually encouraged him to join OKCupid so we could message each other there instead (PMM has a 3-message limit per day for free members). Eh, I figured it couldn't hurt to join, on the off-chance that someone cool might contact me. And it is refreshing to have lots of poly lingo in my profile, whereas at OKCupid I try to appeal a wider audience.
A few related threads:
The Official Poly.fm Feedback/Development Thread
Dating sites - besides OKC...
Poly-Dating: How to meet like-minded people
The Polyamorous Dating Scene