IE blows....any hacker, (or potential one), will attack MicroCrap just because it's MicroCrap. Your company is just asking for trouble unless you have a really involved IT team working 24/7 to guard you against this stuff. I'm just a normal internet user (now-a-days) and I much prefer FireFox. Never crashes...don't get "surprised" by snake sites...and I don't have to wait a 1/2 a minute for the freaking app to load in the first place.
I just wish more SW co's would write for Linux...I wouldn't use MS at all!
Browser Bugs constitute the tiniest of reasons for a machine getting trojan horsed or malware affected or whatever for a "reinstallations" you talked about. It depends on who uses a machine and what way.
As regarding Bugs...Search how many and how serious have been detected in IE and FFox. You will know the answer Regards