Windows is designed to be secure (don't laugh). One security measure is to lock users out after a certain number of failed login attempts. Vista, however, tries lots more times to login than you might think. So, even if you mis-type your password once or twice, Vista might think the KGB is trying to break into your laptop and lock you out.
I know this because, 36 hours into a 7-day trip, I appear to be locked out of my laptop.
Now, I can unlock my laptop in seconds by logging in while connected physically my network. Only problem, my network is 1100 km away and I won't reconnect to it for a few days.
So, great, at least my laptop is secure from someone who knows my UID and password. Of course, if someone ripped the hard drive out and connected it to another machine, he could read the unencrypted parts without any problem. Since I would like to keep the laptop intact, and it's the encrypted parts that I kind of need right now, it's inconvenient, to say the least.
When I calm down and I don't want to beat the Windows Vista team lead over the head repeatedly with my laptop, I'll explain why this "security" only matters if you aren't actually a malicious hacker, and why if you are a malicious hacker it's irrelevant. In other words, what I'm going through at this exact moment is much like the people lining up for crosses in Monty Python's Life of Brian: it'll only hurt if you're honest.