One issue I have with Microsoft buying timed exclusivity is due to their development approach. It leads to the XBox 360 being the lead platform while technically it always makes more sense to have the PS3 as the lead platform for games. PS3 lead development results in more efficient and portable code which benefits any modern platform including the 360 and PC. Using Microsoft's recommended coding techniques lead to more sub-optimal performance and significant porting issues for non-Microsoft platforms.
One of various developer comments regarding this topic:
Bioshock dev team: "So instead of declaring a "lead platform" and porting the game to the others, we’ve instead changed the game engine so that all platforms look (to a programmer) more like a PS3.
This means implementing a task-oriented task processor… that mimics the PPU/SPU split of the PS3. Writing code this way is more difficult for us, but has a key advantage: it’s both optimal for the PS3 *and* gives speed improvements on other platforms."
