I've been limited to reading reviews so far, but from what I've read ICS is a significant android OS evolution.  I like the idea of flicking through files, for example, a finger flick while reading an email takes you to the next (or previous) message.  Small thing, but nice.  The voice text input is supposed to be much better, although better than mediocre is damning with faint praise.  

One thing I find really cool and potentially useful from an everyday security standpoint is the face recognition feature.  Having my smartphone just look at me and unlike sounds really convenient.  I read that it can be fooled with a photo of your face, but at least it will keep co-workers from snagging your phone when you are away from your desk and taking photos of their feet.  Yeah, I work with some odd people. 

Probably the thing I'm most interested in from a practicality standpoint is the data usage function.  It is a toll that lets you see exactly how much data you are burning through, when you are doing it, and the amount used by individual apps.  Over a year, this feature alone could pay for a portion of a new ICS phone for me by preventing overages.  

There is an article on ICS that you might like:    

http://www.pcmag.com/article2/0,2817,2396527,00.asp#fbid=xEzz3lFTOW_