Now, maybe my situation is atypical, but my experience is that the disk defragmenter built into XP is pretty hopeless. It takes hours and hours and hours to run each pass and requires several passes (at least) in order to get anything useful done... and even then it's iffy. I went looking for a better solution and ran across Diskeeper. They had a 30-day trial available, which I went and tried. I really liked it. It happens to be the defragmenter that Sandia has site-licensed. I wound up buying a full copy for delivery via download.
It worked great. Unfortunately, early last week a few things went badly wrong on the configuration for my laptop (not Diskeeper's fault, more like DLL, driver, and registry hell) and I had to reinstall Windows from scratch. Since I had to rebuild anyway, I got hold of a copy of XP Pro (thanks, Lars!) for the better network stack. All went reasonably well until I hit one snag.
See, the download for Diskeeper gave me the complete registered binary. It isn't the usual unlockable shareware where you type in your code. Unfortunately, the binary I had downloaded was long gone in a hard drive crash. (You might guess that I've had some bad luck with this laptop recently.) I wrote to Executive Software telling them what had happened, giving them my order information, and asking if there was anything they could do for me. Then, just to patch things in the meantime, I downloaded the 30-day trial... and discovered that the version I had bought only runs on XP Home. If I wanted to keep using the software I'd have to go up to the professional version, which still costs a reasonable amount of money, but after a long and frustrating night that was not what I wanted to hear. I wrote to Executive Software again mentioning that and asking if there was any kind of upgrade offer they could make me. At this point I was pretty much resigned to having to buy the software again from scratch.
I was very surprised -- no, make that astonished -- to check my email two days later and find that they had sent me a download link for the professional version of Diskeeper.
I've had my share of frustration and grief from various support centers, both customer and technical, over the years. That makes an instance like this all the more pleasant. I'm very impressed.