I've been a member since 01/2007 and have been developing against their API for nearly as long (though for what I imagine are rather obvious reasons, I haven't been near it recently). I've seen more fail whales than I could possibly count. I've sent 5000 tweets over the last nearly six years. I'm even listed as a contributor in the original O'Reilly book on Twitter API development.
I've seen it slowly become less and less useful and usable. I've watched them make their developers and contributing users hate them as they struggled to find a business model (who else remembers the #dickbar ?). I'm now watching them destroy their ecosystem as they try to execute on their chosen business model.
Twitter, I am disappoint.
Increasingly I think they're no more a tech company than say, Warner Brothers. Warners rely completely on tech for creating and distributing content but it's not ultimately what they produce which is of interest and / or value. Ditto Twitter.