I suppose I should start by telling you what my old favorite feature was... I'm not sure what it's called but it allows you to navigate up and down folders much more quickly. It's great for going from one folder to another at the same level (e.g. from one folder of pictures to another).
My NEW favorite feature comes courtesy of Omar's blog: the shadow copy. Here's the MS description of the feature:
Windows Vista now includes shadow copy functionality built in, which enables users to access previous versions of their documents, even when they are stored locally on their computer instead of on the network. Accessing the previous versions of a file you're working with is easy.
What happened is I was bit by a bug which removed all the date taken information from the pictures I took over Christmas time. Big deal? Not to people who simply print their pictures... but for me it meant all the pictures were in random order on our web site. I searched high and low for a tool to copy the date information from another part of the file and then remembered Omar's post. The process of restoring files was pretty straight-forward... and really made me happy work provides us with Windows Ultimate (unfortunately for home users, it's not available on the consumer version).
For the curious, I made some screenshots of the process:
Oh, also cool: if you get a Windows Home Server your backups on the server will show up there too. Sweet! Dang I want that cool round one! See the Digital Amnesia site for more info (presented in an entertaining fashion) or for a great demo, watch CJ's video interview on 10.
Thanks Vista for the save (and thanks Omar for the pointer 
).