Meh.

I have been using vertical tabs for a long time, through Tree Style Tab (Firefox Extension), which has the additional benefit of tree hierarchy.

I don't see a "everyone should use them", though. People have different usage patterns, number of tabs, amount of parallel or queued work and concerns, or ability to clear out tabs on session end. Many people prefer classic horizontal tabs - whether as a deliberate decision or not.

I certainly prefer horizontal tabs, and by a lot. But I don't think it's the best layout for everyone and every usage pattern. It's good that we have the choice of alternatives.