With Steam Wallet, players can add funds to their account using any method accepted by the service and bank the money for future purchases.
While gamers are still able to purchase items in single transactions using any of the accepted payment methods, the wallet's primary function appears to be the ability to purchase additional content while playing Steamworks-enabled titles. This removes the need to exit to the store's front page to add the latest DLC to your favorite titles. Also, its complete convenience makes the entire feature extremely dangerous for our wellbeing and bank accounts.
The "first of many" upcoming titles to utilize the feature is Team Fortress 2, which today launched its "Mann-conomy" in-game store offering a slew of wacky items for use by any of the game's maniacal classes. Presumably to celebrate the launch of the "Mann-conomy," Team Fortress 2 is on sale for 50% off ($9.99) this weekend.
Wallet funds can be added in increments of $5, $10, $25, $50, and $100. The wallet can be set as the primary source for Steam purchases, or saved for in-game stores only. Users can also combine payment methods when purchasing games and content on the Steam store.
Shacknews recommends that those with an addictive personality hand all credit cards to a loved one immediately.
Checkin' it now, hopefully it's useful :)