I've done some more research on MBAs...
Apart from the $200k loan, another thing putting me off is that an MBA doesn't guarantee success, but then again, I guess nothing does.
The starting salaries for MBA grads is usually quite high (around US$100k for the Ivys), but I read somewhere that around 40% of this years graduating class from Wharton are still looking for work.
I'm still really keen on going ahead, and if I do, I think the next couple of years is the time to do it. I'm still (relatively) young at 26, and hopefully, the US economy should be better placed to hire more grads in 3 to 4 years time.
Harvard would be fantastic, but I think my first choice would be Wharton or Stanford, followed by Chicago, MIT and Columbia. I've heard the Harvard grads can be REALLY arrogant, and that's the last thing I need...
At the end of the day, they're all great schools and I think it'll all come down to which ones will accept me.