Question: I have a 4GB RAM 500GB 7200 rpm HDD laptop and when I hibernate the laptop it takes in the region of 3 or 4 minutes(\*) to hibernate. not the 24 seconds it used to take.

It takes this long whether or not my external USB drives are plugged in.

When I got it it was pre-installed with Vista Home Premium, I have since restored the OS from the backup DVD's I created, and also upgraded to Vista Ultimate.

What should I be checking in order to track down the source of this rather sloth-like hibernate process.

I'm looking to tips, techniques and tools please peeps.

Thanks in advance.

I will be back to update / answer this question as I investigate, and also if I find a solution.

(\*) Timed it - it took 4 minutes 38 seconds.
31 seconds after enabling disk write caching

Answer: 
In my experience, a slow hibernate is a result of write caching that has been disabled on the disk. Have a look at the properties of the drive, under the Policies tab.
make sure hiberfil.sys is a contigeous file (disable hibernation, defragment the drive, re-enable hibernation).