In semi-full disclosure, I don't actually pay for my Gametap sub but I really do think it's awesome. It's weird to see everyone flipping out about what's available this week on the VC or XBL for $5 - $10 when everything non-Nintendo has been on Gametap for like two years. Yes, if you have a PC you have the free emulator alternative, but unless you enjoy managing your coin-op arcade, Genesis, Sega Master System, Commodore 64, Sega Saturn, DOS, and Dreamcast emulators yourself (along with a couple hundred Windows games), Gametap is still a pretty convenient alternative.
Where else are you going to find Freespace 2 and Leather Goddesses of Phobos, people.