1. Not too much, iPhone can obviously call people and text people but other than that, iPhone is bigger and has less memory space.
2. Yes it voids your warranty. I would personally wait just a few weeks to version 2.0 where there is something called the "App Store" it is pretty much like jailbreaking but is legal and most things on it are still free. There will be loads of games made by loads of people as well as big companies like EA and Sega. Super Monkey Ball and Spore are some games. You will be able to access the app store from your iPod over wifi and from iTunes.
3. It's OK, the app store will have this as well and will be better quality.
4. No it's a pretty good sized screen.
5. Firmware updates certain things on the iPod like fixing bugs and glitches to adding things. People downgrade because it is easier to jailbreak on earlier versions. The next update comes in a few weeks with version 2.0. It contains the app store, a better calculator and other cool functions.
6. Possibly in September, but I doubt there will be a large difference.
7. There are quite alot of applications but alot can damage your iPod and are bad quality. There will be alot more apps in the app store and all will be good quality.
8. No only Youtube but virtually every video is on youtube anyway. Also there are some websites that have video sites just for iPhone and iPod Touch. Also some OD services are available on iPod Touch such as the BBC iPlayer.
9. You cannot get viruses on safari (The internet) as there is no flash and you cannot download software so unless you have a jailbreak your iPod will be virus-free.
10. Quite alot coming in the app store such as Super Monkey Ball and Spore. Most of the games from in jailbreak will be there as well as new ones. Just a few shown in an Apple presentation are Band (A music playing game with pianos, drums, guitar, sax etc.), A racing game where you turn the iPod like a steering wheel to drive and more puzzle games.
11. Yes but only if jailbroken.