Personally, I have been very happy with Vista.  Working for Microsoft, I get to hear people complain/bash it quite a bit and there are some things that can be improved but as a generalization I have been very happy with the experience and I love the security features (once I got used to UAC).  However, I am one of those people that noticed that battery life was not as good with Vista as it had been with XP (no hard data, just felt that way).  Recently I heard about a program called Vista Battery Saver that has gotten great reviews for drastically increasing battery life.  Here is the configuration screen:

Basically it turns off Aero and Sidebar (I don't run sidebar by default so it is deactivated in the configuration screen) when the laptop is on battery power and restores them when on AC.  I'll report on the effectiveness of the tool.

UPDATE: I have been using this tool for the last couple of weeks in many situations where I needed to test out the battery.  I would anecdotally suggest that battery life is improved in the 50% area.  Well worth it if you have to rely on your battery in many situations.