I just found this while verifying my email with Tumblr.
The simplicity of the message just shocked me, in a good way. I kept on thinking that is usually to deliver messages directly, in short phrases, to be direct, to the point, and do not confuse the user.
However, using short phrases usually may arise to ambiguities and users confused.
So... is there any study, measurement o approach to this? Which is usually more desired, short phrases or long phrases?
This example is perhaps less about being short and more about being informal and what many call 'design for delight' ( http://52weeksofux.com/post/531355592/design-for-delight ) which is an interesting topic in and of itself.
That said, your question is about the right length of phrasing to use.
The answer is typically 'use enough to communicate what you need to communicate and no more'.
One bit of research in terms of lengths of phrasing in the context of navigation is from UIE called 'the scent of information' ( http://www.uie.com/reports/scent_of_information/ ) which states that being excessively succinct isn't necessarily a requirement as much as adequately communicating your message is.
