I know N900 will never support real multi-touch functionality because of resistive screen. But I would like to add some ideas how to implement it with almost same comfort by one touch at the time.
Multi-touch functionality, like zoom and turn, is the only thing where the iPhone is still better than N900. Why not mimic these actions where it is possible and make N900 more attractive for iPhone users? Let say that one finger touches the screen always before the other. You can perform same actions if the first touch position is fixed. It does not make any difference if hold your finger on this position or you rise it. So you can raise it before making the other touch. The only trick is how to recognize the first touch.
Discussion thread: http://talk.maemo.org/showthread.php?t=41837