Let me give you my two cents on not using IE.
First off, to what LMiller7 said about "Millions of people around the world use IE exclusively."
That is because IE is installed by default exclusively on their Windows computers when they buy them. That's it. Whenever someone asks me to set up their computer after they buy it, I always give them a choice of IE, FF and Chrome and they always choose a browser other than IE.
I personally use Google Chrome web browser. So let me give you the reasons why:
1. Chrome runs in its own
sandbox. Which is a major security advantage in my book. In other words Chrome runs with security permissions of your logged in Windows user -- and I pray to god that you're not logging in as an administrator to your Windows account
Other browsers, as far as I know, IE and FF, run in a "tiered mode" -- they have their "kernel" executing with admin privileges and then the UI part runs on a user-mode level. Which is OK, as long as the browser doesn't have security loopholes in the code, which as we well know, is not the case for all of them. So if there's a new browser exploit in IE or FF that may give some rogue site access to your system, an attacker may gain admin rights to your computer because of the web browser's architecture. With Chrome, all they would get is the same low privileged access as your logged in user. Big advantage in my book.
2. Each tab in Chrome runs in its own process. I know that IE and FF do not do that (at least the versions to date.) The major advantage here is reliability. If one tab becomes unstable, slow, etc. a browser itself, or you, via a built-in task manager can simply terminate the bad tab without losing the rest of your open tabs.
3. Chrome is faster. Hands down. With one caveat though. If you have less than 4GB of RAM, Chrome may take a toll on your system with many open tabs. In my case I have 8GB installed and it runs really fast. In everything -- opening up from a fresh start to loading pages. It's funny. I noticed it many times. Chrome loads Microsoft's own Hotmail page way faster than IE itself on my system
4. Chrome (and FF) have better HTML5 and CSS3 support. For some people it is not a big deal, but for me it's important. For instance, I love those resizable text input windows. Some sites (like this one for instance) have very small text fields. Chrome (and FF) allow to stretch it to whatever size you find comfortable. That's just one thing though. Search for more features of CSS3 and you'll see what I mean. (Although true to say, most CSS3 stuff is supported by IE10 now.)
5. Chrome comes with the built-in Flash. I don't know if you know how many security vulnerabilities Adobe has in their Adobe Flash plugin? It's mind boggling. I'm sure we're all aware of endless updates that they issue to that thing too, hah? There must be a reason for that. So with Chrome I was able to completely remove Adobe Flash plug-in from my system and kill two birds with one stone -- make it more secure and get rid of incessant updates nuisance.
6. Chrome comes with the built-in PDF reader. The same as above, Adobe Acrobat Reader is riddled with security holes. So by using Chrome you can uninstall that as well!
7. Chrome can synchronize open tabs across multiple devices. This feature is awesome! I can work with something on my desktop, then keep all the tabs open, go to my laptop and have them open there. Works across platforms as well.
8. Chrome (or FF) can reopen all opened tabs upon rebooting or in case of a computer crash. I don't know about you, but I keep a ton of tabs open (for sites I've been going through.) So when Windows updates come up, it would be a major pain-in-you-know-what to reopen my tabs when computer restarts. With Chrome (and some easy initial set-up) I no longer have to worry about that. I can simply reboot computer without worrying to close Chrome and when it loads up and I run Chrome it pulls all my open tabs right up.
9. Chrome does seamless auto-updates. All you need to do is reopen it to be up-to-date. It doesn't ask all those questions like FF does, it simply updates and does it pretty quickly too. And it doesn't nag you to reboot computer or log in as administrator.
10. Also, I'm not sure if I can mention it here, if you install Adblock Plus plugin for your Chrome or FF, it will be the best thing you ever installed on your system. Commercials on sites and especially in online videos (YouTube for instance) will be a thing of the past

And, no, it doesn't come for IE.
11. This is very technical stuff, but it's important concerning online security. IE has a bad implementation of Extended Validation for SSL certificates, or HTTPS connections.
Read here, especially where it says "The Trouble With Internet Explorer" in the middle of the page.
Now, why I don't like IE in particular:
1. Bad UI. For instance I have to copy and paste a lot of text. The way IE does it is cumbersome, the selection skips blocks of text and then when you paste it, new lines are all messed up, etc. Not cool! I tried it many times. If I load the same page in Chrome or FF, it copies and pastes without any issues. Plus, IE didn't have any grammar highlighting until recently. No resizable text fields. And so on.
2. Slow. Whatever Microsoft says in their ads, but general sites don't run fast in IE.
3. Really bad gaping security holes in IE prior to IE10. So if you're using IE9, IE8, or worse IE7 or IE6, it's like keeping your backdoor unlocked at night. Seriously.
4. Not complete HTML5, CSS3 support. I should admit that IE10 is very close to be on par with the rest of the world, but still there're some issues remaining.
5. IE is deeply rooted into the OS, which makes the whole system potentially vulnerable for browser exploits.
Well, IE has some pros too:
1. It is the only web browser that is supported by an enterprise/corporate environment. For instance, its seamless integration with Active Directory's Group Policy restrictions is very good.
2. IE10 seems to be quite nice (UI mostly) when running as Metro app on Windows 8 tablets.
3. Some older web sites run in IE only, so you need to have it in the background... just in case. Well, not that you can uninstall it either
