I have currently have a soft spot for Lucida Sans Unicode (Body text), Trebuchet MS (captions and small-print) and Georgia (headings). 
Alex, if you can handle the ClearType issue (or whatever anti-aliasing system you’re using), give Constantia a spin. It’s a lovely serif font, and it’s slightly smaller size gives it an additional elegance.
Damn Microsoft for releasing a clutch of truly excellent fonts, and then sabotaging them by making them CT-dependent.
For anyone who doesn’t already have the new C-fonts, I think you still get them when you install PowerPoint Viewer.
I forget now, but there’s info in either my article or in the bibliography (in the forum discussion) that gives you info on obtaining the Vista fonts. (Actually, C-fonts is more accurate, because Segoe UI is not included in most downloads, which is too bad, it’s a great font … except for that ClearType issue.)
Yup. I’m not sure why that is. Segoe is lovely. I really like the light version.
You also get them with Office 07 for Mac. 
I made an executive decision not too many designs back…after doing the (huge amount of) research for that article, I decided that the number of people who both have the Vista fonts and have ClearType or other anti-aliasing disabled is relatively small. Since then I’ve coded with a Segoe UI-driven sans stack and a Constantia-driven serif stack running the show. Both stacks look really good to my eye. It’s a tradeoff, but I think it works well for the Vista and MS Office 2007 users (who have CT auto-enabled), giving them fonts they don’t always see and that look good in a design. Admittedly, I’m always a bit uneasy with that decision…
Max, In my new look web design I’ve decided to take advantage of the Microsoft Office 07 font’s because their not only available for people using Office 07 for Windows and Mac (and their free viewers), but it’s also included within Windows 7 (as well as Vista) which means their usage numbers should be increasing on a consistent basis (making them relatively websafe now if you compare them with other typefaces). I will always provide fallback’s for them but their worth using at this stage as there’s a good chance a fair number of people will have access to them in some form. At least people who use the Vista / Office07 / Win7 font’s will have some ClearType style anti-aliasing tool automatically enabled by default so while it is a trade-off it seems to be a reasonable combination to expect. Before Windows 7 I would have agreed with you (in terms of the fonts being too low in use to support), but now I would argue it’s the best time to start using them 
I plan on using Constantina and Candara as my sans-/serif mixture
Candara is not my favorite of the Vista fonts, but I’ve never tried a design around it. I can see it looking quite nice as a body text, especially in a relatively small size. Since you’re a pretty smart fellow, I’ll give it a second look.
This website shows Candara in action on the web and I think it looks pretty good (Calibri felt a bit too condensed for what I’m after), perhaps Corbel would be better?
To my eye, Corbel works well as a wide sans, much like Verdana, while Candara has enough “flair” in its design to work in a situation where you’d normally use Trebuchet.
Not sure I agree with the font stack for the site you link:
candara, tahoma, geneva, sans-serif;
But you’re right, the site looks nice in Candara.