I've had a few new problems with Steam lately too. I shutdown my pc before Steam was ready for me to do so (how dare I) and when I rebooted steam.exe was gone. Completely gone, and Steam could not start. Steam support answer for the error was invalid although full service was eventually resumed by Windows System Restore (Windows in rescue shocker!).
Now everytime I try to close Steam it delays saying it is syncing with the cloud even though I was just playing a game that is not on Steam cloud. Even after this, when I go to reboot, Windows tells me that Steam is still doing something and delays the reboot. What on earth is Steam doing these days? And please stop it.