I'm typing this on ICS after using iPhone exclusively for nearly three years and can say I'm rather impressed with it. It is no longer nothing like the G1 (that I got one to play around for few weeks back then) or the Nexus One. It gets a lot smoother, prettier and third party software feels a little bit more likable (UI-wise) than it used to be.

Compared to when I last looked where rooting is prohibited by manufacturers, today we have something like HTCdev that provide an official way to unlock that is kind of cool.

Judging from the one in my hand right now I'm giving it about 85% of iPhone smoothness which makes me seriously looking forward to Jelly Bean. It would become my primary mobile OS of choice if Google finally get vendor update and manufacturers crapware sorted out.