Running your Windows machine or any machine for that matter should always be carried out with a LUAP (Limited User Access Privilege) i.e. a NON-ADMIN Account!!
The problem is most people don’t and this is predominetly due to Windows default logon from a factory install CD as Administrator.
Is it a pain to run with a non-admin account, well not really, there are a few tricks and tweaks that you can make. Perhaps if you are using a machine for Games only, then you might have an argument.
Take a look at this blog from Aaron Margosis of Microsoft