I must admit that I signed up, waited a few weeks, got impatient, eventually forgot about it, and then one day, 3 months later it came through!
It’s definitely worth signing up for. There are products out there that you can buy that provide the same sort of info should it be something that interests you.
I agree that it is slightly limited in certain areas, i.e. it only shows the top 5 search phrases used to find your site. However, the ‘site overlay’ function looks pretty cool. It shows an image of your site and the popularity of the links on the page. You can easily see graphically whats working and whats not.
Do put your name down but be prepared to wait a while…