I vote with Nergal and ishan_rulz.
I prefer CCleaner as a safe utility that errs on the side of caution.
If anyone wants more thorough cleaning, use a different cleaner.
You can get more aggressive (dangerous) cleaner for FREE.
You do not have to spend $100 to remove more junk.
Just $19 will give you death by a thousand cuts - or you could have got it for free on 11 August at
http://www.giveawayoftheday.com/2009/08/11/
Every day I visit www.giveawayoftheday.com to see the "special for today".
If I think it might be useful I visit in the morning ready to download and install etc etc.
If it is is another file / registry cleaner I visit in the evening to see how many people have managed to get back on line after re-installing Windows following a disaster caused by "today's free bargain".
I have suffered daily BSODS all the way from DOS 3.? through to Windows 98.
XP is a lot better.
I do not know if it is better at being error free, or better at concealing its errors to reduce Help Desk work load ! !
I always expect a BSOD.
I am able to HOPE a simple file deletion or registry key deletion that is interrupted by a BSOD or power failure will either cleanly accomplish its task, or cleanly do no damage at all, and a normal reboot will follow.
I have no such hope for any defragmentation that involves moving stuff around.
I would fear that a BSOD might interrupt in mid-shuffle, and there might be no reboot if vital items are not in the expected places.
When I see the defraggler forum I hear a voice - "Beware all ye who enter here" ! !
I admire those adventurous spirits. They may appreciate a registry defragmenter.
I use ERUNT which makes a registry backup each morning.
When I wish to remove "empty space" in the registry I will use NTREGOPT,
BUT only immediately after a clean reboot and a fresh registry backup so that if a BSOD trashes the registry I can immediately restore from the ERUNT backup.
Alan