What you need:

• You need the latest PR1.1 update (software release 51-1)
• You need the ISync plugin from the link below.
• You need to enable bluetooth dial-up-networking[1].
  Follow these instructions or install the Bluetooth DUN app from Maemo extras devel (or maybe it is now in Testing already)

That's it. You can get the plugin from garage homepage

Disclaimer: This plugin is not an official plugin from Nokia, try it at your own risk, it might destroy your data. Please make a backup of your data before giving it a go.

What should work:
* Contacts (all fields supported by the N900, expect im and voip usernames should work)
* Calendar
* Tasks

What will (currently?) not work:
* Notes (the "standalone" ones; contacts notes work fine)
* Synching via USB

[1] DUN is only need for the very first synchronization though, so that ISync can identify the N900 as such.

Edit: Removed attachement and instead pointing to the new project homepage.