This email from iTunes just popped into my inbox:

"Did you know that if you've purchased one or more songs from an eligible album, you may now be able to buy the rest of the album at a reduced price? You have up to six months after first downloading a song from an eligible album to purchase the remainder of the album."

This was hinted about just the other day in a New York Times article.

Update: Here's a BusinessWeek.com article on iTunes new "Complete My Album" feature. "It now gives a full credit of 99 cents for every track the user previously purchased and applies it toward the purchase of the complete album. For instance, most albums on iTunes cost $9.99 so a customer who already bought three tracks can download the rest of the album for $7.02."