What about recommending a potential matchup to your friends? I don't use dating sites, so this might be out there already.
In short, what if I'm looking at a profile and think, "hey, this would be a good match for my friend XYZ." The mechanics of it could allow me to set my friend up with someone, basically allowing me to act as an agent on behalf of my friend (initially).
Alternatively, you could do a take on the double-date idea. Have people with friends post a double date, where your user fills in the 3rd/4th person depending on the calculated compatability of friends (for this, you would need to answer a few questions about your friends... which would make their signup seem slicker and faster).
