A brief history
Dart attempts to address the issues of GWT, whilst still remaining a general purpose programming language. For an example of what Dart can do, take a look here.
Rule #1: The complexity of a project is a function of the number of languages used to implement it. 23 languages is too many*, 1 is perfect, but most projects are somewhere in between. (Don't ask about Rule #2. I haven't got any other rules yet.)
In 1997 Sun launched the "Java World Tour" to promote Java to every developer they could reach. This had a significant impact on the adoption of Java. Dart may need to do something equivalent to win developer's hearts and minds, whilst continuing to ensure they deliver the right technology stack.
For the Dart project to succeed the team must learn from previous work, listen to developer's needs and try to win over hearts and minds. If they get the balance right they could transform mainstream web development. I'm cautiously optimistic that I can soon get back to developing systems with 1 language, even if it's unlikely to be SmallTalk.
Update: This tweet on #dartlang suggests more server support will be announced at Google I/O in June.
* Yes, I worked somewhere once where 23 languages were used. I also worked on a large scale SmallTalk project where 1 language was used.