I can't decide whether this is in explanation or apology for the fact that gmail is crazy slow.
It's also possible that you find gmail awesome because you're comparing it to an in-house system. I'm not. I'm comparing it to Asana, Quora, StackOverflow, or even other some GOOG products. In my world Gmail lines up with JIRA more often than with the tools whose performance consistently delight me.
Maybe it's the JS? Gmail is very code heavy and my laptop sometimes can't keep up.