I've seen the $0.69 albums and their subsequent 20GB Cloud account upgrades, but I just got one for free thanks to a bum transaction. This is similar to the free Prime account posted a while back requiring a canceled transaction.
I tried to download the album Uprising by Muse for $0.69 using the "Buy MP3 album using 1-click" button, and since I didn't have 1-click enabled in my Amazon settings, I got an error message and an e-mail saying my order had been canceled due to lack of payment. However, I got another e-mail saying my recent purchase qualifies me for a free 20GB Cloud account which I verified at my Cloud page.
My best guess is:
1) disable 1-click in your account settings
2) buy $0.69 album using the "Buy MP3 album with 1-click" button
3) receive error message
4) receive two e-mails, one w/ error and one w/ 20GB qualification
5) verify 20GB upgrade
Hopefully this works for others, but worst case scenario you're out $0.69 and in for 20GB for a year.