I've been having the same problem and by accident discovered that my spacebar short cut didn't work if I had my Firefox browser open. So if you are running Firefox by any chance while working in Photoshop CS5 - close it. I ran Safari instead and the hand tool works if that browser is open.
I was running Chrome side by side with Photoshop CS5 and it worked fine until I used the Anesidora extension on my chrome. I disabled it and turned Chrome back on and my spacebar shortcut came back!
I just closed and opened my browser again and it worked fine for me, i don't think is necesary to stop using any extension, just try restarting your browser.
I am using Photoshop CS5 on Mac OS X Lion. I have been experienceing the same issue when using Chrome. However I have never used the Anesidora extension.
Just thought I'd add this. I closed my browser and reset my settings with no avail. But restarting my computer (MacBook Pro) fixed this issue for me. Point being, if your lazy as me and turned to the forums before rebooting your computer, save your time and try a reboot before deleting your settings.
I just upgraded from CS5 to CS5.5 and it happened to me when I had Safari open. I quit/re-launched Safari and now get the spacebar handtool function. I tried to recreate the problem, but it hasn't happened again.
Same Chrome browser problem, only my problems seem to start once I log into LastPass as of this week's LastPass update (July 2012). If I restart Chrome and don't log into LastPass, I can still use my spacebar grabber hand. (I am in CS5.5.) Not sure exactly what that conflict is.
Close Chrome, check PS, AI, InD to see if spacebar shortcut works, then re-open Chrome. All good - no need to restart (which is what I used to do until I thought "....there has to be a better way").
