I installed ICS on my Nexus S, it was pretty cool but there were a few things I didn't like.
1. The app draw was laggy.
2. The stock browser. It doesn't load the whole page? so when you look around it has to load the part of the page you are looking at, so you are presented with a grey square or blurry text while it loads. Also, if I do something else on my phone when a webpage is loaded in the browser and then go back to it later, it has to reload, it doesn't stay in memory. Both these things are, to me, very annoying. Oh yeah, and the keyboard can be very laggy when used to input text on a big website, like youtube or a forum.
Because I like to use dolphin (which uses the stock browser) and not opera, I went back to gingerbread and am much happier.