Blogger doesn't have the fanciest web interface I've ever seen, but it might just have the best.
Obvious, but complete. Nice little touches (like changing the title on the preview page) but nothing that messes you about (unlike Microsoft's Outlook Web Access, which inhabits the opposite end of the usability spectrum, where you find those things built by people who don't use them themselves). Fast. Uncluttered, and yet I can't think of anywhere where I can't directly do what I want. It even looks good.
One notable omission is the lack of any spelling checking; I guess they're all Mac users too, enjoying the fact that Cocoa checks everything they type, as they type, all for free. Even if it does mean that "Blogger" is marked as a misspelling. [Update: it turns out there is spelling checking, and a very pretty implementation too, but they still lose a point for using an icon that doesn't stand out anything like as well as the other functionality, and which relies on US cultural knowledge for its meaning. And to think I almost gave them an extra point in the previous paragraph for not using any icons!]
I wonder how long it took to get to be this good?