If you're really close, then no I don't think it's a good idea -- because then you have to start relating to them in a totally different way. Too many speed bumps for my enjoyment.
If you're not best friends, then by all means bang bang bang
Yep. I was friends with my 1st girlfriend then we dated for 3 years. I was friends with my 2nd then dated to 6 months. I was also friends with my 3rd and we're now engaged.
Congrats. For some, it works. I guess I have mixed feelings on it. I agree with Taps a lot on this one. But then at the same time, it gives you a good foundation to build on. I'll admit it's never worked out for me thus far though.