I use my iMac for email, web, youtube.com, iphoto, the odd iMovie and the odd handbrake movie. Its 4 years old now and recently the HDD sounds like an airplane is taking off - so time to buy a new system. If I get the basic Air with 4gbs - Can i leave it on all night with the screen off ?? Will it get too hot if I leave it to do a handbrake encode ???