Just a quickie note. I'm a designer. You wouldn't know it from the site I posted here last week, but then that was about code, not design, and CSS ain't my thing. Most of my design work is in print, especially food packaging, brochures, ads; but I've also done art for the sides of buildings 120ft wide. If you've ever bought sushi at a market in the US you've seen my work :\
Anyway, you really get what you pay for with design, and few people who pay for it are actually willing to recognize that. 99designs is great if you're a tight-fisted carwash owner in Dallas or something. And it might be fine if you're just looking for a stupid logo for a template site. Beyond that, you need people who are actually trained to do this stuff.
Basically what's missing in the wide-open "I have Illustrator too" market isn't communication; it's coherence. You hire one guy to do a logo, a girl to handle a header, someone else to do some ads. Or you hire one person but pay them per hour to do each of those things, rather than giving them 10 hours pay up front to come up with a master vision that will tie the mess together.
Any designer who says, "logo, no prob" without noticing that you have no well-laid-out color palette, no consistency in your typography, should be fired before (s)he's hired. They should refuse to do work for you before you figure out what you want. That's how you know you're dealing with someone who knows what they're doing.
I think the concept of pooling a designer is great, if the designer is great; and not great if you end up with a lousy designer. You're still gonna pay hourly. If you're paying under $35/hr., you're getting someone who's unemployed, probably for a reason. If you pay between that and $100/hr., you're probably going to get someone who isn't really capable of art direction. And if your pool isn't capable of that, then you're going to get poor results.