Re: how long is it safe to leave my lappy on?
I think about 3-4 hrs should do it for a laptop on battery power. You could leave it on like all day when you hook it up to an outlet but you might fry your laptop. Try using stand by mode when you're not actually using your computer. It saves electricity, while you have easy access to the computer in case you need later in the day. The new Intel Centrino Core Duos offer excellent mobile performance, with extended battery life. I'd go for that next time you buy a laptop.
Rig -- Emachines T5026, 3.06ghz P4, 300W Bestec PSU, 160 sata hd, 512mb dual channel 3200 ram @ 3-3-5-8, ATI Radeon 9250 pci, dual layer 16x dvd+/-rw.