But we can not argue with its popularity...just strange that people are happy to be restricted to 140 characters. Only enough to express an emotion or give a basic opinion.
Twitter
When I first noticed Twitter I thought it was a load of rubbish, but as I started following people who had similar interests, it opened a whole new world to me. Twitter's Search function alone is brilliant as a service on its own. Just about any major news story of relevance is usually picked up on Twitter first (or published first) but more importantly, you can then follow the development of that major event in *realtime* throughout the event. Add to this twitter's extensions for easy browser or smartphone access and you're good to go.
Also, if any service of any kind goes down, I just search for those keywords using Twitter Search first and if 2000 others have the same problem, I'll see it immediately. No need to check with any company or wait if someone may or may not reply to my own forum thread; I already know whether the problem is only affecting me or not which makes troubleshooting much easier. There are several examples like that which makes Twitter rather unique, since everything is published and read in realtime.
The trick is to "follow" the right people; those who have something substantial to say (and the wordsmiths can actually manage 140 chars easily). I will never understand why anyone would want to follow some celeb who tweets about his toothbrush when in fact you could be following your favourite journo who frequently tweets about the the issues that matter to you, not to mention the 'breaking news' tweets that effectively competes with RSS feeds\. It also gives you access to those people.
EMAIL
As for email dying... perhaps a percentage of teenagers will agree with the author of the article. Email as a business tool is still widely used and very important; I rely on it quite heavily. GMail and filters = magic. Easy to search for important info, can store anything, it's fast and versatile. It's still the first thing I check when I start my day and I don't see that changing anytime soon.
FB
I use Facebook more socially to stay in touch with old friends and share the odd photo album with them but over the last two years I have found myself using Twitter much more than I do Facebook, simply because FB does not provide the wealth of realtime news feeds that Twitter does.
As the saying goes, Facebook is for the people you went to school with, Twitter is for the people you wish you went to school with.
I don't necessarily see these services competing directly with each other though, they all have advantages and disadvantages.