Comment 18 for bug 1055448

You can build it from source. This is relatively easy to do on Quantal now, since v0.98 is in the repos:
$ sudo apt-get build-dep onboard
$ bzr branch lp:onboard
(optionally run: "debian/rules python2" to switch to the python2 version, you'll have to install dependencies manually then, though)
$ ./setup.py build
$ ./onboard <- runs it from the project directory

If you're ready to install, do:
$ debuild binary
$ sudo dpkg -i ../onboard*.deb

We've been trying to switch to python 3 for a while because of the more consistent Unicode support. There was a lot of pain with translations crashing Onboard. Ubuntu made a push to python 3 in Quantal so we happily went along with this.
The speed hit isn't consistent, sometimes python 3 is ahead, pystone doesn't show the whole story. Onboard can optionally still run with python 2, though.

Do you mean moving the window with the move button? That may go to 100% CPU even on slow systems (custom code to allow it to work with auto-show.). See also bug https://bugs.launchpad.net/onboard/+bug/959035. Since then resizing has become more efficient, but I have no good idea how to improve moving.