It's really easy for technophiles to say "Oh, I could build that in a week", and usually they can. The problem is, nobody will use it. Building a community is really fricking hard - it's the sort of task where everyone says "Oh, I can do that" up until they actually try it and then find out that there's a lot of subtlety to it they've completely missed.
Same goes for Reddit, and Twitter. Those are two other sites that are cloneable in a weekend, but nobody will use your clone.
The combination of the news feed and tagging people in photos (and having them show up in the news feed!) is facebooks secret sauce
Two upmods. Hmm. At least two other people think your question a good one. Okay. (EDIT: Three now)
Well, websites are closely associated with many of the topics in computer science. There are, for instance, programming languages, algorithms, data structures, etc, involved in producing a website, no matter the actual content of the website. Likewise, many computer science professors have classes with names like "Software Engineering" which have large-scale projects similar to real-life projects.
Hope I cleared up the confusion.
Frankly, I don't even like it. Whose aesthetic ideal is responsible for the decision to show pictures at a size other than the maximum (up to a practical limit)? Show me the full-sized picture. Just seems obvious.
What exactly does this have:
http://flickr.com/photos/mongol/515509897/in/photostream/
That this doesn't:
http://flickr.com/photos/mongol/515509897/sizes/o/in/photost...
(Obviously, you could put the various widgets next to and below the above picture with plenty of space to spare.)