Do not update to iOS 6 on touch 4g. You will regret it. Here is why:
If interested in the free ram usage on my iPod touch 4g:
iOS 6.0: 80mb
iOS 5.1.1: 140mb
IOS 4.3.2: 137 mb
(Took along time to downgrade and restore back up to iOS 6)
I got the average ram after a respring and after clearing the memory 3 times but iOS 6 couldn't free the memory so average couldn't get a little boost like other iOS versions. I got the free ram numbers from sbsettings and sbsettings is not fully compatible with iOS 6 so that might of been a factor.
I defiantly noticed the lack of ram in apps. It's the first iOS version where stock apps crashed on me. Settings and the app store crashed 5 minutes in. (I always restore when I upgrade so that is not the problem)
I hope I gave you some insight what is going on with iOS 6.
I might update you guys later with better results when sbsettings is compatible with iOS 6.
I doubt it changed much with 6.0.1 firmware. Hopefully 6.1 makes device smooth with more free RAM and some new features for once. Although 6.1 beta's have been lame.
iOS4 was smooth throughout. iOS 5.0 and 5.0.1 was a laggy crashing mess on touch 4g until 5.1 made it smooth again. 5.1.1 brought back some of the crashing though which I'm currently on.
Honestly iOS6 offered nothing really new or exciting (Passbook literally could've been an app in the App Store like Podcast). Do Not Disturb and Panaroma could've also been a minor update for 5.2 (like the camera icon shortcut was added in 5.1). I also dislike some of the layout changes:
-Music app. In iOS6 everything is white so it is painful to look at.
-App Store and Itunes. iOS6 layout is bad because you can't see the rating (# of stars) unless you click on the app. Also searching is worse because it only shows a few at a time. So can't quickly scroll lesser known apps or underrated ones.
-Apple Maps. Although it works decent in US, worldwide is a bit of a mess. Not having Street View or transit info is less features. However once Google finishes the Google Map App (and Apple allows it) this 'controversy' should die down.