I've finally signed up to Twitter to see what the fuss was about. I have resisted until now because I am allergic to the whole "status update" thing, which seems to be Twitters raison d'être.
So far I like it. It is a handy way to quickly poll your chums for information and it is a useful way to share information without blogging it or circulating an email (push is soooo 20th century).
I am slightly disturbed by the mechanism though: 140 chars (20 less than an SMS) of plain text and nothing else. They almost left SMS out of the GSM standard because they thought it would never catch on, they certainly didn't expect people to sent them to one another, but in Twitter we have a system barely more sophisticated than Telex being run on computers immeasurably superior to those of the Apollo program. This is a not a product concept I would have seen any future in, and yes it doesn't make Twitter any money (yet), but I like it, and so do many other people.
It is very similar to the iPhone debate that rages in our office. Most of us have them and love them dearly, but the conversation invariably centers on the things we don't like: battery life, failed phone calls, lost contacts, buggy email client, miss timed appointments, timezone support, etc... This is exactly the list of things I would have put on the whiteboard as "must haves" if I were handed the task of making the next generation mobile device. Yet the large amount of hate is outweighed by an even larger amount of love (see The Internet for details).
In summary, two hugely successful products that I really like that I would never have bet on. This is unlike successful products that I don't like, which I can write off as "appealing to the uneducated masses". My consumer product radar appears fundamentally broken.