I got scared to death to run anything that didn't need to be on when I was in Florida, with electricity bills running right around $250.00/month for a 3-bedroom, 2 bath cinder block beachside home.
So I bought one of those Kill-a-Watt outlet meters which displays energy used, and plugged in various items around the house to see what they drew. Egad! I switched all the lights to twisted tube flourescents, and all the residents of the house know to turn off not just lights when they're not in the room, but also televisions and computers.
I even put my HP LaserJet 4 on a Sansui audio timer unit so it only runs from 8 AM to 8 PM, but that's still a bit much to keep a fuser warmed up. I may just sell it and use my Tektronix Phaser 780, which goes into Energy Star mode after 30 minutes of non-use. My wife thought I was being a pain in the posterior, but she now runs the washer and dryer during off-peak hours, and I do the same with the dishwasher. I've been rewarded with an electric bill that's now between $125-$150 each month, considerably better than the $180.00 we first had when we moved to Wisconsin, and I'm not done doing energy conservation tweaks. We have one of those 6-clear-globe incandescent fixtures over the sink in the master bathroom, 40 watts x 6 bulbs, hmmm....
As for too much fragmentation, I suppose that's possible, but my dual Xeon IBM Intellistation M fragments the Windows XP Pro boot drive pretty darned hard even if it stays on. No biggy, I just schedule Diskeeper 9 to do a defrag and paging file cleanup every time I do a cold reboot. The IBM is also an electrical pig, so it gets turned off when not in use, although as bulletproof as it is, with the jet-engine thrust case fans and everything else, I'm sure it would work just fine 24/7 for several years. They even gave me a power button lockout insert, so that the machine would power down and wake up only via command from a sysadmin.
My Linux boot drive is pretty much untouched.
I have one of those hard-drive removable cartridge things with key lock, and just swap them out to change operating systems. It's a carry-over from when I was a directorate security manager in the Air Force.