I know for a fact that Games For Windows Live is the reason that Bioshock 2 crashed on my computer three times, including one time when it crashed in the process of saving my game.... It didn't happen after the GFWL patch came out. When GFWL updates either itself or a game, it fires up every core of your CPU to 100% for the duration of the download/extract process. That's totally unnecessary and is the result of terrible, terrible coding. Additionally it utilizes the CPU during normal gameplay significantly more than Steam, meaning that your games have less CPU time available. The GFWL out-of-game window is un-risizable and generally irritating. If you have a computer without GFWL and install a game needing it, it will fetch the v3.0 of GFWL, have you sign in, and then prompt to update afterwards.