Last time I checked neither Safari, Chrome or IE ran on Linux. Opera is not in the Ubuntu repositories. Also I couldn't do without FireBug or AdBlock+. I am only qualified to speak for myself, but I expect I'll be using Firefox for a while still.
I've been running the chrome alpha on linux for a few days and haven't had any major problems. (Although it would be nice if it could import bookmarks.)
Chrome is in alpha for Linux.
And it's excellent and rock solid too. They've started talking about a beta and marking blocking issues in the public bug tracker: