I work in consulting, and have interviewed a number of MBA candidates, as well as directly worked with people who went on to get their MBA. I have to say, my attitude might be a little pretentious, but there's a LOT of misinformation in this thread. I have a tendency to state my opinions as though they're facts, but if nothing else I hope this helps give perspective from someone who can say he's worked with a lot of people that are/were smarter than him.
1. The name matters. A ton. I think an argument could be made that name and prestige will actually matter more in the future for MBA graduates. Think about the number of MOOCs coming out. Think about the amount of content that can be learned online – for free (or minimal cost). The point is that these days anyone can say they know something, and probably actually know it. Then consider how many MBA programs are out there today, especially online – Devry, Phoenix, etc.. Add it all together, and you can see how top MBA programs function as a screening tool for ultra-competitive business fields. If someone is good enough to get into Wharton, they're probably deemed good enough for an interview within PE/HF/IB/Corp-dev/etc.. If there's all this noise within the MBA arena, I'm willing to bet that school rank will be the way employers cut through it. You can also substitute “investors” for employers in the prior sentence if we're talking about entrepreneurial graduates.
2. Accreditation doesn't matter, because if you have to ask whether a program is accredited, you probably shouldn't select it. Again, my opinion here – but I think there's a lot of truth to that.
3. Cost – The cost of a top 10 MBA is not significantly higher than many programs in the 20-100 rankings. I say this because if you're going to take on $50k/debt for a program ranked in the 50's, you're better served dropping $75-100k on a program ranked in the top 10.
4. Network – Outside of prestige, this is easily one of the largest reasons to go big with your MBA. You get to work on projects with people who will also go on to work for big names – or start their own companies – and you get in to alumni networks.
At the end of the day, I'm sure we've all met dumb people with Ivy League MBA's – I know several that are remarkably uninspiring. Is the knowledge gained from an MBA at the University of Illinois that much different that Booth? Probably not. However, the fact that Booth is a top 10 (usually top 5), and U of I is in the mid/high 30's makes a world of difference perception wise. If you're going to do an MBA, I'm of the opinion that you should go top 10 or bust, if you're paying for it. If you've got an employer paying for it, and there's historical precedence of where an MBA can take you within your organization, then a top 50 is probably okay. Anything less in either scenario would be a waste of money (if it's my money), or time (even if someone else is paying for it).