Can't think of much that they could include in 4.0 that I don't already have in my JB 3.1.2. I would like some GPS or network based profiles for ringers, notifications etc. But that alone won't tempt me to upgrade. I am really happy with my phone right now.
I don't need multitasking all that much, but I can use backgrounder if I need to.
I don't rely on the standard SMS app .. I use biteSMS and love it
Lockinfo for the Lockscreen (I can reply to SMS and Mail right from the lockscreen now)
I theme my phone using winterboard. Illumine is excellent and very light. Does not slow the phone down at all.
I get that JB'ing isn't for everyone, but most everything that peeps want is already available and under YOUR control .. not Apple. So you can set it up the way you want. I'm sure some peeps can be intimidated by the process, but it's very simple. As is installing the apps. etc.
Didn't mean to derail this thread, so my apologies to the OP.
Here are some of the packages I use on my phone that require JB:
Activator - I can use gestures on the screen to launch apps
backgrounder - multitasking
bitesms - replacement sms app
Five Icon Dock and SB - more icons per screen
Lockinfo with Lockweather, Clockhide, WeatherIcon and 2do PLugins
PopUp Blocker - get rid of all the annoying popups and better privacy
Notifier - gives me status icons for sms, mail, phone, IM etc
SBSettings - quick access to toggles for BT, GPS, antirotation etc.
Lockscreen with Lockinfo
Springboard Themed
SBSettings