There definitely is noise in there. I only follow about 121 people, which seems like a lot, but really that's about 20-40 people that post more than once a day. It's a reasonable level and I prune my lists periodically when someone is tweeting too much useless information.

The thing about re-tweeting to keep in mind is that there are circles of people. I know Andy Leonard has lots of developers following him, so if I retweet something he's done, I move it to a slightly wider audience in the SQL world. So don't be afraid to re-tweet, but think about whose things you forward on. If you're hitting a different audience, send it along.