Ultimately, with Ubuntu One now being the subject of a big push by Canocial, I would hope the N900 will get support from this (I am also a fellow Ubuntu user and ditched Windows a couple of years ago).

Since the release of Lucid a couple of weeks ago a lot more people are trying to get onto Ubuntu One than ever before and this is causing a lot of problems with capacity. The Ubuntu One team are working on this, so I suspect over the next few weeks this is all they will be doing. After this though, and in fairness their team is very fast and hard working, they will start to look at other things. Phone syncing is in beta on Ubuntu One right now but the N900 is not supported.

You can add your support to this group - https://bugs.launchpad.net/ubuntuone-client/+bug/512052 - and hopefully the more people who do this, the more likely it is the phone will get supported.