Curiosity got the better of me, and I actually cracked open the little Software License Agreement booklet that came with the free "Up-to-Date" 10.1 upgrade.
Actually, there is no specific 10.1 license agreement. The agreement that came with 10.1 is a word for word reprint of the software agreement that came with the 10.0 retail package (otherwise known as X 1.0).
So all the same restrictions apply -- one copy to one computer, single backup copy, not making it available over a network, blah, blah, blah.
I'm sure applying the 10.1 update to multiple copies of 10.0 is an acceptable bending of the rules, but posting it to a public network might draw the attention and ire of our favorite zealously litigious fruit company. But as stated earlier, a "cease and desist" is probably the worst that can happen.