I know from my experience, for every regret I have - every mistake I've made, something good has always come about, too. I have to go looking sometimes, though.
For instance, my divorce is definitely a regret, I wish I'd been able to make my first marriage work. But if I had, then I wouldn't have such a wonderful husband now, or my rambunctious 4 yr old!
on the other hand, I've sometimes wished that maybe I had married David (my now husband) first. But if I had done that, then I wouldn't have my 15 and 9 yr old kids! Plus I have some really great memories from my first marriage, of good times we had before things started going sour - and I wouldn't want to have missed out on those, because they helped make me who I am today.
I think it is just a question of, what do we regret, how would we have changed things, and then what would be different - but not better today?
Hope that makes sense...