Something I didn't see on 555's good list: holding the pen if you have (or want to upgrade to) plus scales.
The hook works a bit better for this, but really the corkscrew works well too.
You can see what I'm talking about on about the 11th post down on this thread.
http://forum.multitool.org/index.php/topic,42283.0.html
From the list above... look at these four things:
extracting fuel filter when repairing an engine
extract the stub of a spent candle from a candle holder
extract plug holders from IKEA furniture
remove cotton wads from pill bottles
This, to me, illustrates the real value of the corkscrew. Removing corks from wine bottles is just one instance of a general class of situations: the need to manipulate something you can't get a good grip on.
There are also times when I'm glad to have it so I can close it over cordage to get a better or less painful grip: tightening boot laces with frozen fingers, pulling paracord or twine tight when doing things like tying stuff on top of a car or setting up a clothesline, lifting hay bales by the twine, etc.
So, all my 91 mm SAKs have corkscrews because it is a good general purpose pokey-grabby thing. I do need to poke and grab things from time to time. When I need to work with a Phillips head screw, the can-opener/small screwdriver works fine, so in my book it's a pure win to go with the corkscrew... no loss of functionality, because the can opener works fine as a Phillips (better than the T-mount Phillips in a lot of situations), and I get a pokey-grabby thing, a storage slot for mini screwdriver, and a micro marlinspike.