As for uninstalling, reinstall the bootable backup/clone or Time Machine backup you made for each machine before installing the upgrade. What? Don't have any? Then, get a bootable, external HD (preferably FireWire, since it's 40-50% faster than USB 2 and designed for data transfers) for each machine, make a bootable backup/clone before updating/upgrading, and ensure that it's bootable and works like the original. That allows you to revert to the previous good state without having to reinstall anything. See these for details:
http://docs.info.apple.com/article.html?artnum=106941
http://www.macmaps.com/upgradefaq.html
http://www.macmaps.com/backup.html
http://www.thexlab.com/faqs/installswupdates.html
http://www.thexlab.com/faqs/backuprecovery.html
If you only have a Time Machine backup, insure that you can reliably restore it to another disk/volume/partition before updating/upgrading.