Hey now guys, no need to be pushy. He's entirely withing his rights to test the program for awhile and see the benefits over time.
Unfortunately, there is no way to remove this popup besides purchasing the program. However, you are free to continue using the trial for as long as you wish. Take the time you need in order to assure yourself of the value of WindowBlinds. I would suggest purchasing an Object Desktop from www.stardock.com instead, since it comes with WindowBlinds along with about 25 other programs, for only 50 dollars. Hope you hang around WinCustomize alot!