Why doesn't my iphone 4s show up in my computer?

You mean it's not showing up in Windows Explorer? I'm not sure why it doesn't do that sometimes either. I think if you have pictures or something like that on the phone, it should show up in Windows Explorer but if you have no media like that stored on the device, it won't show up.

Also I believe the "Enable disk use"/"Use as a hard disk" (or something to that effect) option does not really work with the iPhone/iPod touch.

I don't know if you found an answer but I had this same problem. After searching everywhere on the internet for days I figured it out myself if you go into device manager you will see it in the usb controllers go to portable devices you should see it there also in my case it said under portable devices no driver was installed thats why it wasnt coming up in my computer so I pointed it to a generic driver and it said device might not work then it said it wasnt installed correctly so I unplugged my phone plugged it back in and it installed Apple iPhone again now I have autoplay back and can import all pictures again and it is showing up in my computer again. I figured all this out because I have a 3g and it was working fine with my computer just not the 2 4S's I have. Hope this helps someone else looking for the answer.