I have replaced my HDD with a SSD on my newly purchased MBP 15. I had to reinstall Lion on the new drive and attempted to do a internet recovery. All went well until it asked me for my apple ID, then complained that there is no Lion purchase made by this id (which is correct, because the Lion came pre installed)
I called apple support and I've been told that I was not supposed to see a question regarding the apple ID... When I asked them what ca I do, they kindly offered to send me a Lion thumb-drive if I'm ok with that. Of course I was ok... 2 days later it arrived via DHL...
Back to your original question, theoretically it's linked with the serial number and should be able to re-install it anytime you want...