Hey there,
I just want to clear a few things up. The TodoPaper license allows you to install the application and register it fully on one computer. It also allows you to make 1 inactive backup copy of the software. However, to install it and register it on more than one machine, you have to purchase additional licenses. While this is an extra cost to incur, I am considering discounting multiple license purchases.
As soon as the portable version is released, you (tentatively) will be able to use the software on multiple machines. I still have to work out the licensing for the portable apps and will keep all of you updated.
Hope this helps!