My wife's 3 year old laptop is a ThinkPad T200.  She's been having trouble with it "slowing down" and I finally had a chance to look at it.

Good...gravy. First, 3 years of letting the kids use it (and under her ID instead of making them logon to the accounts I made for them) had taken their toll. Her machine booted up using 3GB of memory.

Second, the ThinkPad coders over at Lenovo should just...knock off the insane amounts of home made junk they throw on there.  I usually wipe out the various "ThinkAdvantage" stuff but hers is the standard setup and 3 years hadn't aged those apps well.

And lastly, and most seriously, is the WinSXS directory.  Her 60 GB hard drive, adequate 3 years ago for her light use (Office, mail, and web surfing) was filled the the brim by a 22 gigabyte WinSXS directory.

Let me tell you right now to save you some pain: There's nothing you can do about it. There is no utility out there that will noticeably shrink it. You shouldn't delete stuff in it. If it bugs you enough, get a new hard drive and start from scratch.  It's a terrible design that remains in Windows 7 and 8.