The new Start Menu in Vista features a power button next to the Search bar. What do you think will happen when you click the power button? Since it's the power button, you would expect it to shut down the computer right? Well too bad that's not the default behavior. Instead, by default the power button is configured to go on standby when you click the power button. Um.. is it just me or does that just not make sense?

I realize Microsoft's goal is to make computing more like a home appliance: shutdown really means standby so you can start up your computer immediately (just like you startup your TV immediately). Personally I use my hardware buttons to make my computer go into Standby, and then use the Start Menu's power button to shut down Windows. So as you can probably guess, I hate how the power button doesn't shutdown my computer anymore. Plus also old habits die hard.
So if you want to change this, you'll have to do the following.
First you'll need to go to the Power Options. This is easier said than done. If you are using the categorized Control Panel, you can get to it by going:
Control Panel > Hardware and Sound > Change battery settings
and no, Change what the power buttons do does not work. That changes what happens with your physical power buttons, not the Start menu power button.
If you have the Classic View control panel, go this path:
Control Panel > Power Options
Next follow this path, which is the same for both Control Panel styles:
Change plan settings under Balanced > Change advanced power settings > expand Power buttons and lid > expand Start menu power button
and from here you can finally change this configuration. Yes, that is a total of 7 clicks just to change the power button configuration! If you didn't follow those steps, take a look at this series of screenshots:



Is it just me or did Microsoft make this REALLY complex to change? I had to dig around for 5 minutes before I finally found this!
And to make matters worse, remember earlier we selected the Balance power plan? Well these settings are per plan. That means if you change your plan, the Power button gets reset to Standby again! You'll have to individually configure each Power plan to make the power button be the same for all plans. Why can't we have a "Override all power plan" option? What a pain! 
One last thing to notice, check out the first Start menu, and then this Start menu:

See anything different? The new Start menu now shows the power button as red instead of the original yellowish color. This is the visual cue that the power button now means Shutdown (red) instead of Standby (yellow). Personally I would prefer if the tooltip would just immediately popped up when the mouse hovers over the button and simplify the message to "Shutdown" instead of "Closes all open programs, shuts down Windows, and then turns off your computer" or "Standby" instead of "Keeps your session in memory and puts the computer in a low-power state so that you can quickly resume working." Geez what a mouthfull!