During the scheduled downtime on Wednesday, April 24, Wizards of the Coast and Magic Online are deploying the next major update to the Wide Beta client. Several points were hit on in Magic Online Business Manager Chris Kiritz's article on the subject. The most relevant information is below:

1. During the Magic Online Spotlight starting during the downtime on May 8 and lasting until May 10 at 10:00 a.m. Pacific, the current client will be disabled and players will only be able to play the Wide Beta version of MTGO.
2. To encourage players to try the new client further, MTGO will be starting Dragon's Maze prerelease events early. Rather than starting at 10:00 a.m. on Friday, like the Gatecrash Prerelease, the Dragon's Maze Prerelease will start at 10:00 a.m. on Thursday, May 9, and will run until 10:00 a.m. Monday, May 13.
3. The current version of Magic Online will be available starting at 10:00 a.m. on Friday for those who prefer the old version.
4. Players who have downloaded the Wide Beta version can use the following Magic Online promo code to get a full-art Dryad Militant: WBSpotlight.

For further information, you can read more about the Magic Online Beta and Magic Online in general in Ryan Spain's article tomorrow on DailyMTG.com.