I have a Macbook Pro right now, so I occasionally plug in my external hard drive to backup things. But Time Machine is built to do hourly backups. When I buy an iMac, I plan on having Time Machine running all the time so I will have that 1 hour backups thing going. My question is how do you guys use time machine on your desktops? Do you keep an external hard drive on all the time (doesn't that waste power?) or do you partition the internal HD (if the hard drive fails, you're screwed)?