I'm in a shell most of my day when not in meetings. I love being able to have a nice full screen with vertical and horizontal splits (Cmd-D or Shift-Cmd-D) with thin lines between each split. Also iTerm helps me keep my hand off my mouse and when I do use my mouse iTerm makes my usage very efficient (double click to copy text .. Cmd-V paste, right-click lots of stuff right in your face on the spot..)

I'm less about tabs and more about splits, with two 24" monitors and my 13" MBP on my desk I can have lots of text space to work with and very little window distraction from window chrome.

Maybe it's just because I'm old fashioned and I love to live on the command prompt (vim -vs- sublime all day long) and I grew up in the era of TTY's and 300 Baud modems.. iTerm feels more natural then Terminal.app, it feels like a terminal someone would use all day long -vs- something you hop in for 20 seconds to type some obscure OSX command you cut-paste'd from some site.

In the past I ran into dumb emulation issues with Terminal.app like wrapping and stuff that didn't work right. iTerm seems to be a "programmers" terminal more then a simple utility to get to the command line.