The thing I like most about flickr is not its openness or RSS support or community features. They’re all great, but the thing I like most is its lack of handholding. This, to me, is the thing that differentiates it from older sites like Yahoo. It treats its users as being a bit savvy. Not complete geeks, but people who’ve used a website before.
In particular, the use of language. The Creative Commons page was down a few minutes ago, with the message “Creative Commons is having a Massage”. When you log in, it will usually say hello in a foreign language (sometimes “Aloha Mahemoff”, sometimes “Hola Mahemoff”). There’s usually some randomness going on - the front page shows different photos, the tag page highlights different tags. Even the layout seems to change if I’m not mistaken, at least on the front page.
This might all seem pretty innocuous, and the language even a bit pretentious, but I like what it all says. Many large websites have been too heavily inspired by misinterpretations of Jakob Nielsen and others. Nielsen has urged people to use simple formats, plain language, and so on. However, this was meant as a general guideline, and should be taken in the context of the time Nielsen began writing: mid-90s, when the web was new to many people, even computers were new to many people, and the pinnacle of web creativity was blinking text and mouseover surprises. The advice was never meant to cause every website to end up looking like google or yahoo.
Flickr shows how to be simple without being simplistic, straightforward without being condescending. Can that sort of design help them build a loyal fan base? Ask Apple.