Sure it can work. I met my current girlfriend on the internet, on a dating site actually. It's gonna be two years in a month and we've been living together since last october.
Dating sites are also an excellent way to find sexual partners.
I tried dating in many different environments and internet is by far the one I have enjoyed the most.
When I first joined a dating site, I really thought that only desperate attention whores signed up in there. (I thought it would be easy sex), but I quickly found out that in 2007, many normal, and even pretty cool and serious people use them.
I also like the fact that it goes straight down to business. No wasted time, both person know why they are there for.