So far I have found it to be very interesting. It does have its share of issues, but overall it is very flexible. The basics are easy to get nailed down in a couple hours, but the more advanced things take a couple days to really get the hang of. However I am new to MVC so that is where most of my learning curve was spent.
It is definitely worth a look. I'd recommend that anyone trying to do advanced things be pretty familiar with PHP and MVC design, or plan on getting familiar.
There are plenty of resources for help at the website:
http://silverstripe.com/community-overview/
I've used the tutorials, but the best help on more advanced things are found in the forum.
I'm still interested to hear what others think, keep posting.