Well I've had an account on here for several years.. 8 or 9? I almost exclusively use it for easy access to my artwork when I'm talking to people and they ask to see, because I obviously don't carry around my originals wherever I go! It's also good to just "have" and see who comments or likes your stuff. Sometimes you can find pretty awesome groups to feature your work in, and some will often have cool contests or inspiration projects that are a lot of fun to do, and gets the wheels moving.
I was more active in the beginning and had quite a good following (or I'd like to think I did hah!), but I left my account sitting for maybe 4 years and it kind of died. I think DA has changed a lot and definitely isn't as popular as it used to be, but like I said, it's just great to have to randomly pull up and show people.