IE is certainly a consideration one should ponder and after giving this quite a bit of thought, I can only conclude
I friggin' hate IE!
What a rotten, stinkin' miserable piece of crap!
I hate that browser with a passion. In all fairness, I'm not as "anti-Microsoft" as most of my compatriots but when it comes to IE, my zealotry is limitless. I hate that damned browser. It's caused me no end of pain in its lack of support for standards. Unfortunately, as the lowest common denominator, we've no choice but to pander to it. How incredibly frustrating.
Side note: anyone else notice how they said their users don't want tabs but they're adding them in the latest version?.