Will backing up using time-machine also backup all the users? I have two users on my MBP, and IIRC, both are Admin accounts. I want to upgrade to Lion GM, and have the dmg to do that. However, to be safe, I want to have a backup. I am not familiar with Time-machine, being new to this ecosystem and all. 

Will running a backup from an Admin account backup all the user accoiunts on the machine? Is it a 1:1 backup?
Time Machine backs up an entire drive/partition/volume unless you specifically remove files and folders under "Options".  All User accounts are included unless you uncheck them in Options.

All of this info is available in your Finder Help menu.