I didn't know that this happened, but let's say that I'm logged in as the local administrator on a server. I download and install a bunch of programs. I delete the installation programs and stuff from the server and then I log off. Months later, I log in to the server as myself, because I'm running out of space on my C drive and need to clean some things out. I delete some log files and old windows updates, and empty the recycle bin. DID YOU KNOW that I only emptied the recycle bin for my own user account?
I never really thought about it before, but it makes sense that the recycle bin is not shared space. Each user account on the computer has its own iteration. Personally, I keep my recycle bin cleaned out pretty regularly, but I'm aware that some people use it for.... longer. As an aside, shame on you if you use the Recycle Bin (or deleted items in Outlook) as somewhere to store things you actually want. I've seen this.
If there are more than one user account on the computer, then you could save tons of space by emptying EVERYONE'S recycle bin all at once!
For Window XP, Vista, and Server 2003 operating systems, use this command:
rd /s c:\recycler
For Windows 7, Windows 2008, and 2008R2, use this:
rd /s c:\$Recycle.Bin