Yeah, I'm working in a real estate office now and an astounding number of sites aren't W3C compliant and require IE! A big part of it is incompetent IT departments and management that doesn't know any better. One of the major insurance companies in the US still required IE6 (!!!!!!!) to access 'secure' employee/administrator areas.They are all flawed. I use firefox till I get pissed then chrome for a bit, then back to firefox. I use IE for the F'ing websites that only work in IE. Man I hate that.
M$ does cache a lot of data, including SSNs, CC#s, etc. There's a program you can run that will scare the hell out of you with what M$ has stored on your computer, but I don't recall the name.
Eli