Benefits - it gives Vista access to more memory, obviously. Disadvantages - Vista will never require 80gb+ of memory, a small simple 4gb memory stick is more than enough.
You probably won't be able to use your ipod for readyboost as you need fast flash memory for it to work. You can find a list of readyboost compatible USB memory here: http://www.readyboostmemory.com/ The benefit of using readyboost is that your PC will run faster if you have less than 2GB RAM at the moment.
Yeah. It's a hard-drive, which ReadyBoost doesn't accept. It uses flash memory to speed itself up, if it worked with hard-drives then they would use the hard-drive in your pc And, even vista won't manage 80gb memory usage
The ipod touch still has a hard drive, you need fast flash memory for readyboost to work. take a look here for Readyboost compatible devices: http://www.readyboostmemory.com/