I first knew my now girlfriend at where I used to work, didn't know at the time of course, but she then went away to uni for a bit, I regretted not getting her number although I didn't know her that well then, but we had talked a few times.
But at the end of her first year she came back for the summer and we went for a drink and found that we had alot in common and she became my best friend, so we went out more and more, little realising we were falling for each other, until later in the year it happened. two and half years later we are still together.
So what started as a drink is now like this.
Sometimes it is worth taking a chance, yes it was a big risk but in this case it was damn worth it. It also depends how long you know your friend, because the best way is to get to know her more before deciding whether to make a move.