The log-in screen is sparse - that's true. We're getting a (possibly slightly biased) 30% conversion rate from it, so it does push people to give it a spin. Same idea as the Twitter landing page. What you get as soon as you log in is a wizard which takes you through the first steps to maximise the probability of engagement.

37Signals wrote a very interesting post on results from their A/B tests on the landing page for Highrise (result, the shorter the better) http://37signals.com/svn/posts/2991-behind-the-scenes-ab-tes...