Hard to believe I know, but Sony's console is a lot less locked down than Microsoft's. Being able to use whatever hard drive I wish, Sony's willingness to allow third party networks into PSN and not being charged a fee to use my own internet connection made the PS3 a clear choice for me. I also like having my online purchases tied to my account and not the console, as well as Sony's rather liberal 5 console install limit (great for game sharing, something Microsoft frowns on)
As well, at least I can be sure my PS3 will be available when I need it. Microsoft knowingly sold defective Xbox 360s for over 3 years until a class action lawsuit forced them to fix the problem. Doesn't make the 360 look like a very good investment to me...