I am now using Windows 7 since its beta release and so far my experience is awesome. But as a developer the hard drive space is always been a problem for me, no matter how many external drives or other stoarge devices you have connected to your machine but the disk space on the host machine is always a primary problem. Windows 7 is more stable OS in Windows family so far (I found it more stable than Win XP) and the reason it is being more stable because everytime you install a program on your Win 7 machine, it automatically creates a snapshot of the host drive. This is because if anything goes wrong with the program or it just crashes causing problems, Windows 7 can recover automatically from that state with the snapshot created before the installation.
But these snapshots hogs up a lot of hard drive sapce and there is no way that you can copy them and place it in a different drive or just change the location of the snapshots been taken by the OS. Therefore to maintain the balance, the OS automatically deletes the last/oldest snapshot from the hard drive resulting some free space for the user and for other processes of the system. If you no longer require the snapshots (only if you think that your machine is running perfectly fine) execute the below command to delete all the snapshots created so far:
c:\>vssadmin delete shadows /for=c: /all
In the above command /for parameter should have the letter of your Windows OS drive. In my case it is C: (as in majority of the cases it will be C:)
Just in case if you don't want to delete all the snapshots then instead of using the /all parameter use the /oldest parameter. This will dleete the oldest snapshot from the drive:
c:\>vssadmin delete shadows /for=c: /oldest
This will free up some GIGs of space if you are using it for the first time and if you are using it quite frequently then also you end up with MBs of free space.