Logging on as Administrator is a bad idea...
For your day-to-day activities, that is. The blog post below points this out one more time:
NEWS: “Removing end user admin rights eliminates 92% of vulnerabilities"This advice holds independent of operating system, version, etc.
I do believe though that Vista's User Account Control (UAC) provides significant security and usability benefits by allowing people to easily provide administrative credentials or elevation of privilege to selected processes.