Hello dlowan
Sorry, I noticed when previewing this post that the A2K system changed the salutation that I originally typed to "debbie", a moniker that I know you hate to be addressed by. It will not allow me to change it back, and I beg your forgiveness and request your understanding in this matter. Now on to my originally intended post:
In addition to the previous suggestions, you may wish to take a gander at this page from the Microsoft Most Valuable Professionals site:
http://www.mvps.org/winmac/usertips.html
Although it hasn't been updated in a while, it seems to still hold true in large measure.
Knowing that you spend a fair amount of time on your computer, I have a concern that in addition to the normal accumulation of junk files on your system there is a danger of "unfriendly" items hiding in your machine as well. I am assuming that you already have, and regularly use, a good antivirus program, but such a program will not root out various spy and usage tracking elements that are oftentimes installed in your system without your knowledge and consent; oftentimes when you install a new program. I would recommend installing and regularly running both AdAware
www.lavasoft.de
as well as Spybot
http://spybot.safer-networking.de/
Both of these utilities are free and have been enthusiastically received in the tech press. They have both been available for years and have proven their stability and efficacy.
The sorts of files and ancillary applications that these utilities go after are oftentimes malicious in nature and serve only to track your computer usage and occasionally will transmit data from your machine to a remote computer without your knowledge or consent. In addition to the security concerns pertaining to this, these "stealth" programs will also suck away your system resources. Ridding yourself of them will not only improve your security but will help your machine to run better as well.
Be sure to read and understand the instructions for both of these utilites because haphazard and reckless usage may have detrimental effects.
There are a variety of programs which will help to clean and optimize your system more effectively than the native Windows utilities. Most of these, however, are not free (the aforementioned items being among the exceptions). I have recently read of a free "cleanup" program called BeClean which was recommended by Fred Langa (whose expertise I normally respect) as being the culprit in the trashing of many trusting readers' hard drives. Sometimes in this world one does indeed get what one pays for. If you wish to explore nonfree cleanup and maintenance utility options I will be happy to assist.