if you find a seed in a bag of weed, then somewhere a female was pollinated to produce one. Most likely it came from the same female you are now smoking. I just got one seed from a quarter i recently bought, whcih is a little strange cause if you have seedy bud you would expect more than one to show up in a bag. maybe dealers try to pick out all the seeds so that their buyers won't know about them, or so they can keep the seeds to themselves.

as for the potency question, most people think that pollinated bud is less potent than the normal stuff, but other people don't think it makes much of a difference. the stuff i got that i found a seed in was super strong- my stoner friend said it was the highest he had ever been. so i dunno if seeds=less potent bud...