Sorry to break up this IE bashing, FireFox/Mozilla loving get together.
If you did some actual research you'd find that 94% - not 80% - of the people online use IE as their browser. If you want to develop a virus or trojan, take a big guess at which browser you're going to target?
Furthermore there are more people scrutinizing over IE looking for flaws on a day to day basis than there are people who actually develop Mozilla, let alone look for flaws in it.
If you switched over to another browser from IE because your PC got infected with spyware, adware, viruses, etc then that only goes to show that you are either uninformed on how to keep your PC safe, or don't care enough to bother.
I've never used any other browser than IE and I've yet to come across a single piece of unwanted software on my PC in all those years. My mom - who is completely clueless about computers - also solely uses IE and each time I come over her PC is completely clean as well.
Why? Because she will actually bother to stick with the common sense tips that I gave her. "If you don't know what it is, click 'No'". "If someone forwards you e-mail with an attachment that doesn't end with an extension you know, ask me and don't open it."
The sad fact is that most people (and that includes people here I'm sure) will happily click "Yes" should "Do you want me to install and destroy your computer?" come up and then go on to scream that their OS/browser/email application/take your pick is insecure.
Firewalls, virus scanners, adware removal tools are the last line of defense. The very first and most effective protection tool you can ever hope to have is your own common sense.
If you can't spare 5 minutes to go through IE's settings and secure it, then you have no right to complain. There's a blog from a Microsoft employee dedicated to how to minimize the issues you'll encounter when running as a limited user account vs a full administrator one as well which should block mostly everything serious since most of it is written with the assumption that it'll have free reign.
Critizing Microsoft for not shipping IE with its default settings already secure is a whole other topic for discussion. The bottom line is that they didn't, it's not hard, it takes but a few minutes and you only have to do it once.
All that said, competition is a good thing and I do believe Microsoft is wrong in halting IE's development until and only for Longhorn since it's web standards support is either outdated or just plain broken.
Everyone is free to use the browser of their choice, but do so for the right reasons and don't get swayed by all the hype and media misinformation.
People also need to learn to take some form of responsability. Microsoft doesn't go without fault, but neither do they. Your day to day spyware/virus/spam pests are 100% preventable.