Several years ago some friends got married in Vegas by an Elvis impersonator. I had a kitscherrific time, but wedding-wise a few things went wrong:
1. At those Las Vegas wedding chapels they schedule ceremonies back to back. If someone, like the bride's sister, is running late they might miss the wedding all together.
2. Having the dinner at a casino's buffet might be funny, but eating in a generic banquet room with no decoration, no music and terrible lighting is depressing.
3. The best man and maid of honor need to understand that they have to get up and make a toast. It doesn't matter if they're shy or can't think of what to say; the night is not about them. If they don't toast, no one else will and then the happy couple won't get to hear how much everyone loves them.