I will admit it did make RSVPing a lot quicker, in that I didn't have to hunt for an envelope and make a special trip to the post office to buy stamps
I completely agree with this. I never have stamps and would have to make a special trip to the post office. And while clearly this isn't a big deal, it just makes it easier for your guests to simply fill out and send back. I'll definitely be putting stamps on mine, I think the $30 postage that may be wasted on RSVP cards for my wedding would be the least of my worries regarding my wedding costs.