I've been using Zen for a few months now and love it. There are some rough edges (the article mentions how customizing it is confusing because multiple mechanisms affect different parts of the app). However, it's getting regular updates, and once it's set up, it's really a pleasure to use.
Apart from the elegant, minimalist user interface, I particularly like how it implements workspaces. It makes it super easy to switch between personal and work contexts.
Same here. My main gripe has been address in the latest update - the icon! The old stylised 'Z' just didn't look a like a browser icon when alt-tabbing, and I had to think about where my browser is, rather than instinctively going straight to it. At this point my brain only seems to accept that browser icons are circle-based.
The vertical tabs and side-by-side tabs are fantastic
Apart from the elegant, minimalist user interface, I particularly like how it implements workspaces. It makes it super easy to switch between personal and work contexts.
I highly recommend it.