There's only one Admin account, and nothing else.
Leaving yourself wide open to viruses/trojans/spyware/adware/malware/etc.
The whole point of having restricted privileges for user accounts is so that your system doesn't get screwed up. This harks back to UNIX systems where mainframes were used by multiple people, many of whom could easily fuck things up as they don't have a scooby what they were doing. Its a heritage that continued in *NIX systems, but was only really adopted by Micro$oft with I think XP. Most people see it as a hinderance and then get frustrated when their computers end up slugish because of all the malware shit thats been installed.
Unless your developing web-pages and
really need to use IE to ensure your sites work with all browsers I can't think of any reason not to ditch IE completely. Its a piece of piss to import bookmarks from IE to Firefox (might be slightly more hassle to copy all your cookies and passwords over mind).