Just to add,

I remember at Uni, they had set all the labs to take a fresh image off the server EVERY time a machine was turned on!!!

This had positives and negatives. The positives are that no matter what we did to the PC we knew all we had to do was turn it off and on to have a fully working system again. They allowed nearly full priveledges to the machine as again as soon as it was reset it was taking a new image. Lastly it meant that they had almost no requirement for tech support.

The negatives were that if the machine crashed at all and you HAD to reset it you could wither wait 20 min for the image to finish, or move PC's. The latter was not always an option in a packed lab... Aditionally there must have been alot more wear and tear on certain components beacuse of that policy, and it meant that they ALWAYS left all the PCs on, even though the lab was closed from 10 at night until 8 in the morning, causing a bigger electricity bill.

I can definetely see the advantages of having a server image to install incase of infection if you're a company, and i can also see the point of attempting a clean if you're a home user.