My iPod touch 4g came shipped with iOS 5.1. Using for a week, it was smooth as butter and I don't remember any crashes. I was quite happy because I did some research with many saying lack of RAM made it crash often. Also tested 2 iPod touch units at an Apple Store and seperate electronic shop-seemed fine. I finally installed 5.1.1 thinking it would be a minor update and not slow the device down. After installing I had my first crash on Safari and I remember my eyes opening wide I regularly close unused programs. Been using over a month and the device would crash 1-2 times a day only on Safari (also once on Youtube App Store version). I know 4g only has 256MB RAM but 5.1 did not crash on me once. I did not add anything after 5.1.1 as my contents stayed the same. So for those of you who had an iPod touch during iOS 5.X days, was 5.1 the smoothest version? From what I read it seems to go: 5.1>5.1.1>5.0.1>5.0 BTW I do not have iOS 6 installed as I don't want to deal with even lower free RAM which means less background apps can be used. I must say the past few days I have not had any crashes so that's a good sign.