I tried it a couple of times. It's superb as a basic browser. That's what it's designed to be. Blazingly fast loading times, and fast page rendering too.
But I still use Firebird, simply because it's much more feature-rich with it's ability to install extensions. I'm giving K-Meleon the time to develop some more. It shows a lot of promise, but I'm not ready to use it as a mainstream browser just yet.
Used K-Meleon some time ago, but never got used to it. My biggest gripe was the way it handled bookmarks. I'm not quite sure why I didn't like the bookmarks since it was a while ago, but it was the bookmarks that turned me off. It might be better now after over a year more development. I might give it a shot again.