I've been trying out Flock lately as an alternative to Firefox. Although it's based on the same rendering engine, I've heard that Flock is more stable. Flock is interesting in the way it integrates with the many social networking and blogging sites I use, but since I'm a minimalist, it's not really my cup of tea. It's been more stable than Firefox, but it doesn't support the Foxmarks plugin, so I can't synchronize my bookmarks with it. This put me in sort of an awkward position since all my bookmarks are in Firefox, and although I was able to import them, I'm not ready to give Firefox and Foxmarks up yet. I've heard that it at least supports Firebug, which is another must have for me.
Well, I've been using Flock for a week or so now, and I can really see why some people would like it. However, it's just not my thing, and it finally crashed on me. It's probably Mozilla's fault that it crashed, but I'm now tempted to switch back to Firefox.
In summary, Flock is cool, but I sure wish Mozilla were smaller and more stable. Personally, I blame C++ ;)