Nearly every time I've been "set up", its failed. Never tried online dating.
However, when I've met a girl unintentionally without any pre-conceived intentions in the air, its worked out (meaning a second date) pretty much every time. Its nice that way because sparks can fly naturally, and the chemistry between man and woman can just follow its normal course. Putting that forced or artificial element in there just adds too much pressure, and I've found it more difficult to just be myself knowing that I was put in that situation, and the expectations that go along with that situation, rather than just falling into it.
Now, as far as that leading to a relationship, that's a whole other ballgame. But a few fun dates are always nice!