Aside from the negative comments from the skeptics (who have probably never had a Probiotic supplement), Probiotics are practically essential after taking an antibiotic regimen to replenish the good bacteria. That's actually one big reason that people who don't take them get recurring infections and/or diarrhea after antibiotic treatments, but seldom after those are followed by Probiotic regimens.
Aside from that, regular supplementation of Probiotics in pill form or even a daily yogurt (although the pill will give you MUCH more quantity) help with regularity, preventing yeast infections (which many, many women can attest to), and overall immunity. Yes, it is difficult to prove the immunity part in the long run (especially in the double-blind, placebo controlled studies) because there are so many causes of getting sick (although the same could be said for many other things as well including eating a healthy diet), but people that take Probiotics tend to get sick less often.
I've personally been taking Probiotics off and on for a few years and I have stopped them a few times (either because I ran out and didn't bother getting more or because I forgot) and I could definitely tell when I wasn't taking them... I had more gas and more irregularity (I know, TMI) among other things.
I'd recommend getting a good probiotic with at least 3-5 strains and at least 4-6 billion viable organisms per dose if not more... you may want to try a higher dose at first to replenish everything right away, too, especially if you've been on antibiotics before. Give it a try for just 1 month and I'm willing to bet you'll notice a huge difference even within the first couple weeks. Oh, and expect loose stools for the first day or two... it's perfectly normal as your body's way of trying to balance itself out and clears up within a day or so. Good luck and I hope I helped!
Health/nutrition classes, personal experience, and personal research in my role as a Product Specialist for a vitamin company