I have a 2011 Macbook Air 13" running the latest version of Lion. I use an external HP 2511x monitor in clamshell mode connected via DVI and also have a wireless apple keyboard and magic trackpad. I've seen the following problem behavior related to computer sleep: 1. Pressing a key on the keyboard does not always wake the computer even though it is configured to do so. I would say that this happens maybe 20% of the time. 2. When I cannot wake the computer up with the keyboard I open the lid and it springs to life but in dual display mode. The computer screen shows the extended desktop but the machine is not outputting the primary screen because the monitor remains in sleep mode (the monitor indicates it does not have any DVI signal). 3. Once in this state, closing the lid to try to go back to mirrored desktop mode and output video to the monitor does not work. Opening the display leaves me in the state above. The only way to recover from this situation is to disconnect DVI, remove power from the monitor and power cycle the macbook air. BTW - other times, sleep will work just fine and wake the monitor up as desired. It doesn't seem to make a difference if I manually sleep the computer or have it sleep using the timer in system preferences. I've also tried varying the computer and display sleep times so the display sleeps before the computer and there is no change. Am I the only one seeing this strange, inconsistent sleep behavior out of a clamshell operated Air? Sorry for the long post - just trying to see if others are having the same type of issue? I've submitted a problem report to HP but I actually think the problem is with the mac because I'm not able to wake it with the keyboard all of the time. Thanks for any guidance.