Installer
Leave it be. These are the installer files that are used if you go to "Add and Remove Software" and "Uninstall" or "Repair" software.
SoftwareDistribution
Run Disk Cleanup. Start Explorer, right-click on the C: drive, select Properties find and then click the Disk Cleanup button in the Properties window. Wait until the Disk Cleanup Window appears. Click "Clean up system files". Confirm and wait until the Disk Cleanup Window appears again. In "files to delete" check all boxes - make sure to scroll all the was through the list, there are ~9 items. Click "OK".
WinSxS
Run dism /online /Cleanup-Image /? from the command line. This will give you a list of commands to automatically clean up WinSxS in a safe way, and the implications of each command are spelled out.
First, you should have been running with this set of updates for at least a couple days, better a few weeks, so you know you do not want to roll back any of the updates.
You can then use
dism /online /Cleanup-Image /SpSuperseded
dism /online /Cleanup-Image /StartComponentCleanup (available on Windows 8, not on Windows 7)
and/or
dism /online /Cleanup-Image /StartComponentCleanup /ResetBase (available on Windows 8, not on Windows 7)
to reduce the size of WinSxS. Be sure to read about the side effects of these commands first by running dism /online /Cleanup-Image /?. You can read more about dism at technet.
DriverStore
I'm adding this one because it might be relevant to some people reading this answer: Look for Driverstoreexplorer (http://driverstoreexplorer.codeplex.com/). It's a tool to remove drivers that you don't need - after a few years there are usually a lot of them. Make sure to read up on what it does before you wrec your system. If you're not sure what it does, don't use it.
%Windows%and not about%Windows%\winsxs. – Tamara Wijsman Jan 06 '12 at 20:59winsxsis the Windows component store. All the Windows components inC:\Windows(including various subfolders includingsystem32andSysWOW64for 64-bit systems),C:\Program Files, and some items inC:\ProgramDataare all hardlinked fromwinsxs. If the tool you're using isn't hardlink aware (and TreeSize Free isn't, nor is Explorer itself), the information you're seeing is misleading at best and downright wrong at the worst. – afrazier Jan 06 '12 at 21:33