After developing custom websites professionally and looking around quite extensively for a CMS to help me accomplish my task more easily, I can vouch for N2 CMS as the most satisfying CMS out there, PARTICULARLY for developers using Microsoft ASP.NET, C#, or developing on the Windows platform.
I have developed websites with DotNetNuke, which is a reference in the ASP.NET world also. DotNetNuke can certainly do the job, but I just didn't enjoy working with it at all. I thought it's administrative UI was a mess my customers couldn't live with and I its programming design was something that I couldn't live with. So after a few months I continued my quest for "the ultimate CMS" for my own taste.
That's when I found N2. I think one thing that got my attention was N2's quality level, overall design and code practices, are all very high, state-of-the-art and professional! It's just perfect for professional developers, particularly those using Microsoft tools and technologies, but really is accessible to anyone. N2 had an extrensive list of features, like most other CMS, but N2 "delivered" what it promised, which was a good feeling...
Although N2's approach that lets you blend its CMS features around a pre-existing ASP.NET website is a real plus, it also lets you build a small website easily, out of the box and without programming skills. It's just the best of both world: easy to use, yet extensible without much limits in the hands of a software developer.
N2 is quite mature and stable, has a nice community to help you when you need it, and after a year or two using it, I still think it's the best for my needs :)