My experience has been slightly different, though I can appreciate the points made above. Also, I can only really speak with any sort of experience on the writing and translation section of Elance.
If you're careful, you can get work from Elance. Experienced buyers realise that this is one area where Asian offshore providers struggle to compete with western English speakers - because they can only very rarely manage a contemporary idiom. Indian English, in particular, has a very "fifties" flavour to it which can be a grate.
That hasn't stopped a lot of subcontinental providers signing up - presumably because they've seen their programming compatriots offer such superb service and do so well. One or two non-native English speakers have even taken to disguising themselves with US or UK addresses and western names.
So, as I've said, many buyers are wise to this, and also wise to the number of people on Elance who are simply no good. I've picked up around a dozen reasonable projects from Elance, mostly website rewrites. The trick is to bid only on projects where the buyer has good feedback and good experience. Also, leave SEO projects well alone. Quality of English often doesn't matter on these, so bid prices can be astonishingly low. Go for the projects that can only be done by someone who has been born into western culture.
Also, talk to buyers before you bid using the Elance PMB - it's a great way of sorting the good ones from the nutters, of whom, as Copyqueen as found, there are a few.
I've actually done some work for Elance itself. The people in charge there are well aware of the problems. While they're unwilling to impose quality control on Elance Marketplace (they make money hand over fist out of it) they have set up Elance Agency, which is supposed to offer services at set prices from approved providers - though as far as I can see it hasn't really taken off as they'd hoped.