I'll chime in here... (since
I actually used them)
I used PRWEB for my second crowdfunding project.
The reason I used them is kinda long-winded (it's interesting and you'll probably go,
"ah, yeah, that makes sense giving them a try..." but I'll skip it just now due to lack of time)
Anyway, long story short...
$60 to get the press release written (oDesk)
$300 to do the press release with PRWEB.
Pretty much zero effect (I did various tracking of links and such). A couple of "auto blogs" regurgitated the article but that was about it.
A $360 "learning experience".