What the others have already said - don't expect anything new design-wise, expect the usual select component updates.
The real question here is what YOU'RE holding out for. If you don't have an exact idea of what you want in your new phone, that the iPhone5 isn't already catering to, I don't see why you'd be waiting in the first place. There's always gonna be something faster and greater around the corner, so if you're just holding out to "see what's next", you can sit there until you're old and gray.
However, since we're likely not going to see a design upgrade for around 2 years, you may as well commit now, and have an up to date looking phone for almost the full time of your commitment. If you skip the 5, like I skipped the 4, and hold out for some "5s" model, you'll only be up to date design-wise for up to a year, since the "iPhone 6" with a likely new design will already be out when you're still bound to the "5s" for the remaining year. As for me personally, the 4s already does all I want it to do power-wise, so at this point, It's really just all about the new design, so I got the 5 on a 2 year contract, I'm pretty at ease now, knowing my phone won't look like yesterdays even after the refresh. (Of course, one can never be certain, but it's highly unlikely they'll drop a new design in the next model, considering the lengths they went through to offer up this one, and also judging by the recent iPhone history).
Figure out what's important to you, if the current iPhone serves your needs, go for it.
I agree, you should know what you want and for me it wasn't enough of a "want" to buy without upgrade dollars.