I have a twitter account that I rarely use, but in the last week, I've had two occasions to use twitter (for work related tasks). On both occasions, I logged in to be presented with a cartoon whale with 'twitter is over capacity'.

I appreciate that having high levels of traffic on a dynamic website can cause problems, but you dont get this kind of message from the search engines, even the smaller ones that have more traffic than twitter.

If twitter continues to get a reputation of instability, it might find itself quickly being usurped by a lightweight facebook type app that does have the infrastructure to maintain a 24-7 service.