I've been using Firefox as a primary for ages, but I keep IE installed and at the ready for the various websites that require it. I haven't tried Safari yet, but installed it a few days ago because I was tired of the Apple updater harassing me about not having it installed at the latest version. I may give it a spin, but it will be a tough sell to replace Firefox as my primary browser.
As a web developer, it's important to have a few browsers available for testing. The larger the site audience, the more options we test. When I was running the website at Switchboard.com, we studied our logs and used general internet resources to identify all browser types and revisions that made up 1% or more of the traffic for testing. Of course, the internet was our business. It would have really hurt if we dropped 5% of our traffic because we put up something that broke a particular browser. I don't think Alembic's business would take the same hit from such an error.
-bob