Over the years I have been in search of a good affordable content management system (CMS) that was easy to extend.
Sharepoint is a beast and targets collaboration more then CMS. Microsoft CMS is anything but affordable. DotNetNuke, well it just sucks.
Sitefinity keeps it simple. From a development point of view it uses all the out of the box features of ASP .NET, so if you know ASP .NET then you pretty much know Sitefinity. Creating your own custom user controls is simple, just create them as normal then add an entry to the web.config to have them show in the administration UI. It uses master pages, so transferring an existing ASP .NET site into Sitefinity is cake.
As with any product I did find one little quirk. Sitefinity has a custom RadioButtonList adapter which changes the default rendering of it. If you are using radio button lists and they are not rendering the way you expect you will have to make your own custom radio button list.