Is it possible to create a system image of N900 (all partitions), so that you can restore it later if you need to (something like Clonezilla etc. on PC)? If so, how can it be done and how long does it take?
(Suppose you need to sell the device, and you reflash it beforehand; but just in case you want to save your heavily customized system...)

Backupmenu
http://talk.maemo.org/showthread.php...ght=backupmenu

it creates images of all app and rootfs except files on MyDocs

OK, suppose I'm sending my phone to warranty (I hope I won't, but just *if*). So if I use backupmenu, restore the phone to initial settings to not break warranty (e.g. uninstall kernel-power, etc), get my phone back, and restore using backupmenu, everything will be back as it was?

I guess yes, because if it backups the rootfs then the SSU, kernel, customized files, installed apps, everything will be back at it's place, but I need a confirmation just in case

It's not that simple I'm afraid. A few people have tried, no one has yet succeeded to clone an N900 without issues. Backup and restore the same device using BackupMenu (BM) works fine, but you must make sure that you have the same kernel on the device before you start your restore as you had before you took the backup. This is because the kernel is on yet another partition that BM does not touch. Any attempt at restoring on a different device is fraught with problems. See for example my experience, and I am sure I have seen some else reporting something similar. Search is your friend.