It's not Internet Explorer.
This is also the #1 reason to use Safari, Opera, or Chrome.
Why not use IE? It's not standards compliant. At all. I've been doing some work on my personal webpage, and I'd be done with the layout by now if IE didn't exist. When 3 out of 4 rendering engines render a page the same way, chances are the fourth one is doing something wrong.
I don't really care if you use Firefox or Safari or Chrome or even Opera. They're all trying to be standards compliant. And doing a good job.
What I care about is that you aren't using IE. Because every person not using IE is another person that web developers don't have to worry about when they're sticking hacks into their CSS to get IE to render it right. If you just switch from IE to something else, you'll be part of making a difference.
The point being: do eveything you can to lessen IE's share of the browser market. I'm waiting patiently for the day when the biggest question about my new website look is, "How bad does it look in IE?"