The start up messages are kernel messages that pass too fast over the screen not giving a human time to read. However they get logged:
dmesg -H or dmesg > boot.messages make them human readable
It is wise to check them to see where Linux has problems (e.g. HW not matching with the Kernel configuration)
dmesg | grep USB
dmesg | grep eth0
If you want to see just the lines containing USB
To delete the old messages type dmesg -c