how to delay boot when waiting for usb disks?

[Martin Kraus <lists_mk@wujiman.net>]

Hi. I need to mount a usb disk during boot so that daemons writing to the disk
start. The problem is that usb-storage takes time to set up block devices and
it does this in the background so it depends on many factors if it makes it
before mountall.sh is called.
Is there some way this can be accomplished in debian without explicit sleep 20
in mountall.sh?

Also, is there some way to start daemons only after certain hardware becomes
available? 

thanks
mk