If you long-press on the retweet button in the new Tweetbot 3 for iPhone, you can retweet that tweet to any other account in Tweetbot. A list of other available accounts appears, and tapping one will complete the RT without making you switch to that account.
Since I run a bunch of accounts for Finer Things in Tech and other things, this is tremendously useful. When I find something in my personal stream that would go great on @FineriOS or @FinerWeb, I can easily retweet it without having to break my reading flow.