Over the past few months, I have been noticing a massive drop in my  
computer's performance, HD space, and totally available RAM.  
(Actually Sarah discovered this, but since its my email, I'm claiming  
credit)

My hard drive was actively reading/writing all the time and general  
performance was dropping.  Also if you go into the Activity monitor (/
Applications/Utilities/Application Monitor.app) you might see a  
process called SyncServer using up a ton of CPU and RAM/VRAM

If this is the case, you'll want to check out this article.  http://
www.eissing.org/iceblog/page/bc?entry=os_x_syncserver_madness

I'm not sure what SyncServer does exactly - it seems to be associated  
with iSync in some way and it looks to me like its got some serious  
memory leaks.  If you don't need to use isync (to sync with a mobile  
phone or .mac or something), I would highly recommend disabling it as  
you'll end up saving yourself some headaches and possibly early hard  
drive failure.

The article is a little vague on how to do this exactly so here are  
the steps:
Open up iSync (/Applications/iSync.app)
Go to the iSync menu (next to the apple in the top left corner) and  
click Preferences
Uncheck the box that says "Enable syncing on this computer" - This  
option was gray for about 2 minute before it let me uncheck it...  
just be patient
Click the button that says "Reset Sync History"
Restart your computer, and while its booting hold down the following  
4 keys at the same time (Apple-Option-P-R)

This should do it, and you should get a good portion of your  
computer's resources back.

-Tim Cortesi