Two striking examples: 1) Last week my girlfriend, by far not a hacker or nerd, said she wanted to join Twitter. She's joined, and found many of her also non-technically savvy friends on it as well. It's becoming mainstream now. Once it starts hitting critical mass, it'll be much harder to slow.
2) Out tonight with a bunch of geeks, and almost every single one has started to use Twitter. Only a few didn't. These are Amazonians, Microsofties, startup folks, etc. That is, these are early adopters. I was shocked by how often Twitter came up in conversation. However, not once did anything about Twitter's downtime come up, and not once did anyone even mention FriendFeed.
So, on one hand you have Twitter beginning to go mainstream, and on the other hand you don't see the early adopter types leaving.