I've been registered and using Box (and dropbox) for quite awhile now.
Just checked and saw this :
What 50GB promotions does Box currently have and when do they end?
Android phones and tablets: Now through 11:59PM on 3/23/12, log into Box for Android on your phone or tablet to get your upgrade automatically.
LG Android phones and tablets: Now through 6/30/12, download Box for Android on your device and sign in to get your upgrade automatically.
Sony Tablet S and Tablet P: Now through 12/31/12, download Box for Android on your tablet and sign in to get your upgrade automatically.
HP TouchPad: Now through 12/31/12, download Box for TouchPad on your tablet and sign in to get your upgrade automatically.
RIM PlayBook: Now through 12/31/12, download Box for PlayBook on your tablet and sign in to get your upgrade automatically.
Sony Ericsson Xperia phones: Now through 12/31/12, download Box for Android on your smartphone and log in to get your upgrade automatically.
Apple devices: This promotion has ended.
Edited again - I only have 5GB - bummer!