Yep, dropped Dropbox for SpiderOak ages ago due to a number of really poor security failings on Dropbox's part. (Remember the day they accidentally allowed blank passwords to login to anyones account?)
Dropbox's strength is the simple and consistent GUI that's available in all platforms (desktop, mobile and web).
I've moved to SpiderOak and it works perfectly for me, but it's not a UI I would recommend to my mother.