Fragmentation hell. Give us a driver updates database and release patches and upgrades to the OS incrementally, not in minor revolutions of incompatible mess. That is my only complaint about Android, version upgrades are coming TOO fast, and with not enough substance added to each new version to truly merit being called upgrades. Counter this with the tendency to make things incompatible as you go, and boom, fragmentation hell.
What they REALLY need is to make tablets based on the Chrome OS.