Well, it was yesterday, anyway. More evidence of Amazon’s willingness to use deep discounts to boost its MP3 Store came with the US release of U2’s No Line On The Horizon. For one day only, Amazon sold the album for $3.99 – versus the $9.99 being charged for it on iTunes. It’s part of the company’s Daily Deal scheme – on Monday, they sold the new Prodigy album for $1.99, while Bon Iver’s new Blood Bank EP went for $0.99 last week.The company announces the deals on its Twitter feed, which has nearly 13,000 followers at the time of writing. It’s interesting to see big albums being treated effectively as loss-leaders to try and tempt digital music purchasers away from iTunes (or, indeed, to pick up new customers).