Mark Russinovich, the security expert made famous by his various tools created at Winternals, has lowered the bar when it comes to Vista. According to him, after the adaptation period while malicious people experiment with Vista, rootkits and trojans will still continue to thrive and be a menace to Windows users. Despite the advantages of the UAC, he brought up a critical point about relying on it too much:

"It's a best effort to raise the bar and stop malware from making changes to the operating system but it's not a security boundary," Russinovich said of UAC, the oft-criticized mechanism that requires that all users run without full admin rights.
On top of that, UAC may prevent system compromise but might not prevent a person from losing their personal data, such as from data-mining adware or password-stealing trojans. Time will tell, of course, but so far the record hasn't been good for the desktop. Will it get worse?