if your pc does that, it's most likely a bottleneck somewhere - a process doing something, to either harddrive or cpu.

But, fortunately, you are running Vista. Open up Task Manager (ctrl-alt-delete - start taskmanager) and under the performance tab, select "Resource Monitor" - put this on your secondary screen somewhere it's not too intrusive. Expand the cpu, memory and harddrive sections, and do a 5box mounted run though a zone you know will cause the problem. Pay attention to the file i/o load on your harddrive, and especially WHICH files are being used. Swapfile usage = drop in performance. Wow does not need to use the swapfile when playing, only when you run out of physical memory. You can see this aswell under the memory section. Also, when the break of /follow happens, see if anything is maxing out right around there.

This was how I diagnosed my setup - and ended up adding 4 extra gigs of ram, and 2 extra harddrives in a stripeset. Those 2 extra drives only contain wow, with symlinking. My fps drops and performance issues / break of follow disappeared like vapor.

Good luck.