March 31st was World Backup Day and as part of the promotion, Spideroak offers an extra 3GB (on top of the free 2GB of free accounts) for all users. Just enter the coupon code on sign up, or once you've setup the backup client, by clicking on "buy more space" button and entering the coupon code then. I assume this works for existing users as well.
More information about World Backup Day:
http://www.worldbackupday.net/
Thanks, just tried it but I think there are two things you have to watch out for. 1. is to check monthly billing, otherwise you get the yearly billing offer for worldbackupday. 2. I'm not sure of but I think the extra space may be only for the next 30 days and you revert to the old limit after. If you don't use any of the extra storage, no harm done, but if you did eat into it, then you have to start paying.
I would be glad to be proven wrong for 2. Anyway I'm nowhere near my free 2GB so I backed out.