I've also been using eLance for work on a project I've started, and expect that I will continue doing so.

My criteria to decide what work to outsource is "will having someone else do this task make a significant positive impact on the project". Generally, I've been doing the coding and outsourcing things that I don't do well (e.g., graphics and certain content). However, I'll probably hire some coders since that should let me add features significantly faster than I currently am able to do.

I'd strongly suggest starting out with outsourcing small tasks at first. Not only to protect you from paying a lot for work you may not be happy with, but also for you to decide if the results produced by someone else are so much better than what you could have done. My artistic skills are bad enough that paying an artist made sense. However, paying an editor to go through the site is probably something that I won't do again (since the gains weren't that noticeable).