I know that you can import from Facebook to Yahoo, and from Yahoo to Google+, but is there any way yet of importing followers and following to Google+ from Twitter?
I wrote a tool to help with this. It can find the Google+ profiles of folks that you follow on Twitter.
It does rely on those you follow on Twitter having a www.gplus.to Google+ nickname that matches their Twitter name.
Currently it will find around 20% of those that you follow, but this can be increased simply by spreading the word, e.g. via tweets, that Twitter users should go and grab their matching gplus name.
At the moment this is not possible. I would imagine that when the Google+ API becomes publicly available to Developers there will be a influx of new Applications that can interact with Google+