You bet they are! Take a look around the web and realize that, in a serious economic downturn, social sites are soaring while many other sites are reporting a slow down in traffic.
Monica from Vtribes.com sent me an article on the subject by Josh Bernoff at Harvard Business. It tells a tale of social applications and their obvious immunity from bad economic times. There are properties online that are hurting compared to this time last year, but social media properties are not among them.
I highly recommend this short read for insight on social media during tough economic times.