Unfortunately, many people are willing to give up security concerns completely for easy functionality. The limitations of dropbox make it easy to understand for someone who has never used this kind of service before, whereas SpiderOak inherantly has more of a learning curve because you have choices - not everything you back up has to be synced, etc.
The challenge posed by the Dropboxes of the world is how to make people care about security BEFORE it becomes an issue - how to play the games of engaging and educating your user base such that they care about the services offered and they're willing to get over the learning curve.
To that end, I think SpiderOak University was a great idea - but it's over. New users should be able to be rewarded for educating themselves about the features and services SpiderOak offers. That's the kind of thing that makes a person willing to engage, rather than just say "That's too much for me, I'll just stick with Dropbox, it just works and that's all I need."
I also really like the website re-design. I think SpiderOak is doing a great job in terms of making the right steps to grow their user base - but it's still baby steps, there's obviously more work to be done. Not the least of which is just advancing the features set: the mobile app is still behind the curve.
Still tho - I could not be a bigger fan. I tell everyone I know to use SpiderOak.