It's not poor form per se, but Twitterr is all about balance. With Twitter, I subscribe to a person not a feed so I'm interested in their thoughts as well as their work.
I like to see an equal distribution of ideas, conversation and links (both your own and other people's).
Can't say I've seen a lot of incoming traffic from Twitter but I do still announce my posts. I used to use TwitterFeed to do this automatically but if my feed got republished in its entirety it would tweet my last ten posts, which was just spammy so I do it manually now.