1. UI built for the era of video and digital photography - It's not actually Microsoft's key selling point, but the thing that everyone will probably find the most useful about Vista is that photos, videos and music are not treated the same as Word documents any more. When you open a folder of photos, they come up as they'd appear in Google Picasa or Apple iPhoto. There's inbuilt basic photo editing. Music folders come up in columns of ID3 tags, a bit like iTunes. Finally, you don't have to rely so much on third party apps to work with your files.
2. Image-based install - PC enthusiasts spend a lot of time installing and reinstalling Windows for their own and other people's PCs. The Vista DVD is actually a pre-installed version of the OS in a compressed form, making it substantially quicker to install. It's also much easier to customise for unprompted installation with the correct defaults, and you can even install your own software automatically at the time Vista is installed - like slipstreaming service packs but on steroids.
3. Up-to-date driver base and better driver handling on installation - Enjoy the just-baked driverbase while it lasts (19,500 drivers large). If you do need to use a special disk driver during installation in the future it won't have to be on floppy disk. Now you can use a USB memory key or CD. Also, Microsoft is now making much greater use of Windows Update for provision of drivers that aren't present in the Windows RTM driver base. Windows Chief Jim Allchin talks about it.
4. Desktop search and search folders built in - Yes, you could already get umpteen desktop search apps including Windows Desktop Search from Microsoft for XP, but you can't underestimate the importance of it being installed on every single Vista PC. Now when your mum rings saying she's lost a document she's been working on all day you can just direct her to the start menu. Also, desktop search folders are handy for finding stuff you haven't necessarily got stored in one folder but that is useful to gather together from time to time (e.g. documents with "tax, invoice or receipt" in them).
5. Sleep mode that actually works. - It's a small thing, but makes a big difference: Vista has finally caught up to operating systems that can sleep near instantly and wake up reliably, in a couple of seconds.
6. Rock-solid laptop encryption - The data on your laptop is worth a hell of a lot to an identity thief. Vista's "Bitlocker" encryption (only in Enterprise and Ultimate versions) does heavy-duty, full-drive encryption, so you can be certain that unless a thief has your password there's simply no way they're going to get in.
7. Better file navigation - Vista now has some time-saving features like favourite folders displayed in the left column of every Explorer window, as well as "breadcrumbed" folder lists allowing you to quickly jump backward and forward through a path. Sure, these should have been put into Windows years ago, but at least they're here now.
8. Inbuilt undelete - Or, depending on how you look at it, inbuilt rolling backup. Every time you make a change to a file or delete it, Windows keeps the previous version. As a result, the "oh !@#$ I just overwrote my entire PhD with Document1" feeling can be quickly assuaged.
9. DirectX10 - OK, this isn't so much a benefit as your hand being forced: DirectX 10 will never be made for XP, and a raft of games have already been announced ‘exclusively' for 10. Admittedly it does take gaming graphics to the next level, but it's very much tied to Vista.
10. Face it, you have no choice - When Microsoft brings out a major renovation to Windows, you can choose to ignore it for a year or two, but then the device drivers start drying up for older versions of Windows, your friends start asking questions about their new PC that you can't answer, and even if you use Linux, you'll inevitably need familiarity with Microsoft's latest interoperability blockers. Face it: your arse belongs to Redmond.