For a very long time my laptop (running sid for a few years now) has been booting kind of slowly. It looked like there was a 2-3 second delay every time a kernel module was loaded, which resulted in something like 3 minutes total boot time. Never bothered me enough, but yesterday I've finally got some time to investigate. After increasing the verbosity of udev logging in /etc/udev/udev.conf I've found lots and lots of messages like this in the log:

Dec 18 00:41:46 droopy udevd-work[425]: wait for '/sys/some/path/bInterfaceProtocol' for 20 mseconds

The only udev rule file containing a reference to bInterfaceProtocol was /etc/udev/rules.d/z60_libccid.rules with the following lines in it:

# last file created by the kernel, if this is present everything should be

The libccid package itself is long gone (I don't remember installing it at all), and the versions of the package starting with 1.3.4-1 (uploaded in February 2008) do not contain this rule. However, the file survived on my system, so this rule was continuing to trigger for every device, even the ones not providing the bInterfaceProtocol at all. Removing the now-redundant file resulted in a dramatic boot speedup (it now takes about 30 seconds), so if you are experiencing similar problems, you might want to check it out.