This is definitely a money-saving option if you're looking for a one-off project. I've met founders who have actually sourced their designs from 99 designs. Purists would frown on that, but I've seen some pretty good work come out of it. Having said that, you need to be really on top of giving feedback and directions to people.
You really have to dig to find good people on odesk/elance (or is it elance/odesk these days?). I find that if you filter by people, locations, etc. really carefully, you can find some mediocre technical talent. If you're looking for freelance writers, that's another story. There are some FANTASTIC copywriters on the site and it's much more affordable and time-saving than searching for someone independently. People will bid on all types of projects -- short- and long-form.
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