I have been very happy with my Nexus One for over two years now, but the news that the Nexus One will not be upgradable to the new 4.0 version of Android put my loyalty somewhat in question. Even though I still prefer the physical look and feel of the Nexus One over the Galaxy Nexus, the larger, crisper display and generally much faster hardware make a switch tempting.
There is nothing really in Android 4.0 which is a must-have for me. The new UI design may be crisper, but no quantum leap in usability. One new feature I like is the tracking and control of network usage by application - a feature, I had been missing since day one.
With its size, the Galaxy Nexus is practically a "phablet" a phone/table hybrid. It is starting to get borderline in size for me to balance on one hand and still reach all the controls on the screen with the opposable thumb. On the other hand, I find myself to do more reading of news articles than before, using some newspaper apps which have started to appear for Android as well (unfortunately, the Economist app does not seem to support 4.0 yet).