I used Conkeror for a couple years as my main browser and really enjoyed the experience. Combined with a tiling window manager (Awesome WM in my case) it made for a really fun computing environment. I felt really cool being able to navigate through the web without touching my mouse.

Like all interfaces, it was better at some things and worse at others, when compared to a more traditional browser. Ultimately, I don't think I was more or less productive with it. Sometimes I do wish I was still using it regularly, especially after I've spent a few hours in emacs.