After installing Sophos Anti-Virus on a number of machines, Internet Explorer was taking three to four minutes to load. After turning on Desktop Error and Virus Reporting in Sophos, I discovered that Sophos was unable to read the IEcache.waf file stored in each user's Library -> Caches -> MS Internet Cache folder. Deleting this file corrects IE, and it then loads in the usual three to four seconds.
The problem sometimes reoccured on some machine; mainly those that had an Explorer cache size set higher than 20MB. So to permanently correct it, delete the cache files and reduce the cache size to 10MB to 20MB. Sophos is currently analysing one of my 75MB cache files that it hangs on reading.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041026180649296