I flashed from 3.2007.10-7 to the new 4.2007.38-2 directly, skipped the 4.2007.26-8 release. Fortunately I did not experience any problems with restoring a backup from N800's own backup tool, like many people here reported with the previous update.

I am most delighted with the improved sensitivity of the touch screen, it almost feels like a new device

Of course it was a lot of work restoring all the apps nonetheless; I made a protocol of all the steps I took for all the applications I have reinstalled by now, including support for NFS and ext2fs. It's intended mainly for my own future reference, but maybe there's some info in there that can spare someone else a minute, too.