In reply to Nico.

Yes. Well if you know any better system please let me know. I haven't found one so far. Even though updating Wordpress does take some time (including backups, checking if everything works, etc), it's still a lot easier and faster then for example Joomla. It's mostly the amount of sites for me plus the hight frequency of updates. If there would be just one or two updates a year it'd already be much easier.