I don’t see this mentioned on any of the sites i normally read so I am going to post it right NOW. So you are running Lion or Snow Leopard and you have Xcode installed through the Mac App Store. The problem is that after it is installed, you have a 2 to 4 GB installer in your /Applications folder. If you delete the installer, you won’t be informed in the Mac App Store when an update to Xcode is released. If you keep it on your computer, you are wasting 2 to 4 GB of unnecessary installer data.
Here are three easy steps that lets you get rid of the bulk of the installer, but still have it show up in the Mac App Store as installed and will let you know when updates are available.
Congratulations! You have now cleared up enough space on your computer to fit approximately 2 minutes of ProRes 4444 NTSC footage on your computer. Of course if you are using your boot volume to hold video footage, you have a bunch of other problems.
February 2012 Update: With the release of Xcode 4.3 / 4.4 Apple has now made Xcode itself an executable application that is updated like normal applications so no more having to keep an installer on the system along with an Xcode install. This applies to anyone running Mac OS X 10.7.3 and above.