This is interesting idea.

N9 as client:
Install: http://cc.oulu.fi/~rantalai/harmatta...emo4_armel.deb

N900 as server:
Fremantle-package all ready has synergy-server (synergys). Only issue will be touch screen, because you can't "move mouse over the screen". There are some use cases for drawing tablets ('wacoms') for absolute/relative coordinates on synergy web page. Let me know if you figure something.