These cards are about to be killed, finally, if a new report is true
Various forms of this rumor have been around for quite some time, dating back to early 2012 when we first heard that Microsoft would be retiring their Microsoft Points currency system in favor of real money. As of today that still hasn't happened, as the Xbox 360 still uses Points as the primary way to purchase games, downloadable content, videos and music, with real currency only reserved for app stores and the Windows 8 Xbox Music/Videos stores.
Now, according to The Verge who cite "sources familiar with Microsoft's Xbox plans", the company plans to fully transition away from the Microsoft Points system with the release of the next Xbox. The virtual currency will be completely killed off in favor of real money across all of Microsoft's stores, while gift cards similar to Apple's iTunes vouchers will be offered that will allow users to add real currency to their account to purchase DLC. As well as the gift card system, standard transactions through credit/debit cards will be supported.
The gift cards and currency stored in your account will work across a variety of Microsoft's marketplaces, if the report is true, including the Windows Store, Windows Phone Store and Xbox stores. Rumor has it that the launch will happen alongside the next Xbox later this year, while an announcement could happen as soon as E3 2013.
Source: The Verge