I've purchased five copies over the years:
1. A copy for myself on release day, 2006. First edition.
2. A Christmas present for my daughter, 2006. First edition.
3. A third copy for myself when my first edition disc was broken by a cat who mistook a pile of hardback books for cat exercise equipment and tried to climb to the top of the pile, which caused the pile of books to topple over directly onto the jewel case containing my play disc, 2009. GOTY Edition.
4. A fourth copy for my best friend, 2010. GOTY Edition.
5. And, finally, a fifth copy for myself on Steam, in case any more cats get the bright idea to try out for The Flying Wallendas, 2012. GOTY Edition.
Of those five I still have three in my possession. Plus Brash bought a first edition the day the game came out. So that would make four total: two first editions (one unplayable), one GOTY disc, one GOTY digital.