So much this. I've probably hosted easily 30-40 different groups or individuals (which is perhaps not a lot by CS standard, but fine, I've done my dues, no?), and I have only been able to surf 3 times, of which 2 were arranged by the attractive young lady I was travelling with (I am not 100% serious, that is sexist, but I suspect this dynamic does play a role). On the other hand, I have frequently sent out 20-50 reasonably personalized surfing requests, depending on popularity of destination, etc. Of course you'll have to take my word that I didn't just copy and paste a one-liner like "Hey I'll be in your city from x to y July, can I stay at your place?", but still, CS is dead to me, I don't even try to surf any more.
Another telling thing is that in many popular destinations (New York most recently for me) the first two pages of search results include predominantly photos of muscular males posing without t-shirts. Somehow I didn't feel drawn to that. :(
Great idea, tragedy of the commons?