The updating process went rather smooth on my jailbroken iPod touch – the main annoyance was the 250MB download (Apple apparently hasn’t figured out diff’s yet).
Once the update is installed, an eventual jailbreak is undone and all “jailbroken” applications are removed. However, my .mobileprovison apps, screenshots, media etc survived – it looks like data loss will be uncommon:
I noticed one more cool thing: when connecting the iPod touch to the PC in order to retrieve screenshots, screenshots made with version 2.2 have thumbnails:
So far, all works well – stay tuned for further info as we get it!