Not less then one column character borders.. It has to burn a column to create borders.. And a couple of other laggy issues.. I need to play with tmux more but when on a bunch of different machines going iTerm straight to the box and using splits makes for a more enjoyable experience.

IMHO Arguing about terminal emulators is almost as religious as arguing about languages. Pick what works for you and I won't judge you if you don't judge me.. Now can we get back to solving real problems.. LOL :-)