Unfortunately for N-Vu, I will always compare it to the more polished, and more expensive, Dreamweaver...

The first killer for me is that Nvu does not edit php files, which is where I live and breath...

From the Nvu web site: "Nvu (pronounced N-view, for a "new view") is a complete Web Authoring System that combines web file management and easy-to-use WYSIWYG (What You See Is What You Get) web page editing. Nvu is designed to be extremely easy to use, making it ideal for non-technical computer users who want to create an attractive, professional-looking web site without needing to know HTML or web coding."

UPDATE:
It appears that with version 1 released in 2005, Nvu development has ceased. The Nvu web site even suggests another open source program if you find Nvu buggy, kompozer. I guess I'll have to check it out...
Also, I've been using BlueFish quite a bit lately, more my speed (supports PHP)