That is very interesting, I had only thought of it in the context of macro.

Its used a lot in astronomy. I keep wanting to have ago but don't have a powerful enough lens. We have clear none light pollutant skies here (when its not raining) just would be wonderful to do

Another program is "Helicon Focus" - I use it quite a bit with CS4 and it is superb.

I use Tufuse Pro and PT Assembler as the front end. PT aligns (among many other abilities) then feeds into Tufuse for the focus blending.

DeepSkyStacker.
This is one excellent program to stack pictures:

LINK TO DDS

After all you can't go wrong with Free.

Also you can go through a well presented step by step guide here:

LINK

Program can handle many formats including RAW.
Be ready to have some fun thing to do when images are getting processed as it may take a while specially with large file RAWs and numerous images in the series...