They give you 15GB to sign up +5GB if you use a referral link + another 5 if you have a .edu address.
I started using it because they have a desktop client for all platforms, including linux. No filesize limits, very easy to use. And they space they give you lasts forever, unlike a lot of dropbox's limited time space. Check it out!
If you sign up through my referral, I get an extra 5GB of space as well. Not sure about the referral link policy, but I didn't see an explicit prohibition and I'll remove it if required.
Just register and download the desktop client to get each of us our 5GB bonus!
https://copy.com?r=Ib9EzI