The "technically correct" way of doing it would be to uninstall it on your current PC before installing it on another (in other words- it can only be on one machine at a time).
The Turbo Tax license is a bit different than most, it is geared towards how many returns that can be done with a particular key as opposed to how many machines it is installed with. I believe the license is good for 2 returns in the standard version.
Somebody's sister in law used someones last year after the someone was done with it. But she couldn't e-file. It would only allow one e-file per license.
This year, someone's wife chose Taxcut because it was supposed to come with better customer support, which it didn't. And someones son was able to e-file after the someone had e-filed.
Just to further assist anyone that plans on using Turbo Tax this year....make sure you pay them any money you owe them directly, or it takes like 8 weeks for you to get your check.