This question's come up a LOT lately -- might want to do a quick search to get the full spectrum of answers.
I'll tell you what I told the others: I know of 2 cases personally. The first is my cousin's wife. She had an ectopic pregnancy after her tubal. I believe it was quite a while after - over a year, I'm pretty sure. Ectopic are the most common pregnancies following a tubal -- it seems the sperm can bypass it, but once it makes connections, starts to divide & grow, and reverses direction back towards the uterus... it doesn't fit any more.
2nd case - the woman got pregnant with triplets within weeks of her tubal. She ended up with 6 kids under the age of 5.