I've had some success doing some online freelancing with Elance. I mostly do database work, and have made about $1000 since i joined in mid-July. Most of the jobs on there are crap and end up going to somebody overseas who will work for $2.50 an hour, but I've managed to find a few clients that are willing pay a decent wage. I've got about three clients that now give me continuous work. You definitely need to put some work into it in the beginning though in order to get clients to pay attention to your proposals, build your profile, etc..
I've had to work a bit though on balancing my side hustles with my personal time. There have been some nights and weekends the last few weeks where I find myself working on free lance stuff when I'd rather be hanging out with friends/family or relaxing. Definitely believe in finding a balance...
One thing I also learned that I just didn't really know before I started is unless you're really confident in how long a job will take you, avoid fixed price jobs and go with hourly only. I took a few fixed price jobs in the beginning, and found myself working too many hours for what I ended up getting paid.
Overall though, i would recommend it, especially if you have a specific savings goal you are working towards. Its been pretty nice to see $1,000 go into our savings account that I didn't originally account for. $1,000 closer to that house down payment!