I use it in two ways.
One is to get my paintings and soaps out to a wider audience, though I keep the spam pretty light. A new painting or various other creation once a week at most.
The other half is to connect with people. You have to put a bit of work upfront and give it about a month but before too long you're connecting with people who share your same interests, keeping up on the very cutting news, and getting a slight thrill when some celeb or other person you admire replying or retweeting you.
I'm actually going to be meeting some twitter friends I just made this next weekend and I'm really excited.