After a recent defrag of my harddrive it suddenly became excruciatingly slow to browse 'My Computer' and other folders with Windows Explorer (explorer.exe) in Windows XP. Sometimes just opening a regular folder with a few files in it would take more than 5 minutes, as well as having explorer.exe hang and be not responding. As none of my other applications were noticeably affected it really had me stumped as to why a regular defrag would cause such a slowdown for folder-browsing, until I discovered that browsing was still near instantaneous when using other file-explorers like Total Commander. Relieved that it wasn't a problem with my drive but likely just a bug in Windows Explorer I set out to find a fix that would bring it back to its old self, but that was easier said than done, and I spent several days searching and experimenting with various fixes.
Apparently many people are having problems with Windows Explorer being slow, and for a host of different reasons too. Most commonly I found the obvious suggestions to run windows update, antivirus, antispyware, defrag and chkdisk, as this will commonly fix the performance and many common issues that crop up on computers that are not kept and maintained by professionals. The next step is to improve performance by adjusting the Folder Options in Explorer. Good tips here are to disable the automatic search for network folders and printers, as well as using simple folder view and to not cache thumbnails. But it didn't make any difference and explorer was still just as slow afterwards. Then I downloaded and ran CCleaner to do a full systems checkup and registry cleaning, and I also removed all recent network paths from my "Network Neighbourhoood" as these things also appear to cause many slowdowns too. Still none of these suggestions made any difference. A thread at Google Answers hinted to NeroVision Express as a possible culprit, but I didn't have that installed of course.
Finally I stumbled across a Techspot thread describing how you by logging in as a different administrator user and deleting the folder "c:\documents and settings\<username>\local settings\application data\microsoft\windows", can fix the problem of extremely slow browsing in Explorer, and this actually worked!
It seems that something had corrupted that part of my windows user profile, but deleting the folder and inducing an automatic recreation of it on the next login fixed all of the problems I was experiencing. Another good thing to come out of this is that all the other tweaks has made the rest of my computer faster too :-)