I still face some problems on my new computer system. One of them iswas that udev was hanging in 8/10 cases at bootup. Thanks to great support from the udev folks I learned how to track it down. I previously tried to add options to /etc/udev/udev.conf (e.g. to raise the log level), but one can actually just add them to the kernel options. This has the great advantage that they don't persist. Things you want to add to debug are:

udev.log-priority=info udev.children-max=1 udev.exec-delay=1

This logs a lot of things (the boot can go from 30 second to minutes, so be patient). The option children-max is turning parallel event execution off and exec-delay is delaying run actions. With those I saw that the system hangs when loading the cdrom.ko kernel module. As I had some problems with the drive as well I swapped it and now bootup is fine.