Just replace "famous people" with people you care about. For example, I follow the tweets of several Firefox employees, the big names in various programming languages, my senators, etc. I do also follow some celebrities, but thinking that Twitter is Tom Cruise in the bathroom just makes you sound horribly out of touch.
Just seems a lot of people use it to follow what famous people "tweet." Want to know if Tom Cruise is using the bathroom? Better check twitter...
If you aren't interested in fame/famous people then twitter has little value.