Patrick's point is that if you have the skills to get users in a business with network effects that strong, there are many more lucrative markets you could crack. EBay, for example. Online auctions is hugely lucrative, orders of magnitude more than dating, and EBay sucks in many ways. But their network effect is so strong that it's virtually impossible to break in.
(Online auctions is #10 on the list, BTW.)
Abandoned accounts and men->women spam.
I think a smaller dating site would prosper quite well if it could eliminate wasting people's time. eHarmony has a good practice in this regard, but eHarmony is also marriage, christian, straight focused - and excluded all others.
A dating site that disabled user accounts that hadn't logged in or responded, initiated conversation eHarmony style, and somehow limited the spam that men send, well... that'd be worth checking out. It would drastically raise the signal to noise ratio.
For spam: perhaps you can only send one message per day to new people, and one message per person per reply. Choose wisely.
Also, for every uploaded picture, grab the date it was taken and put that on the page. Might not stop hackers, but that's a small minority.
Other effects to combat: the ego inflation effect, where having many virtual 'options' makes you more selective.
Maybe even a 'ask a friend' feature, where you email a reply history to a friend and ask their advice (helps with network effects).
There's LOTS of room for innovation here, essentially.
Don't we all just want to be loved?! ;)