The StarCraft 2 custom maps platfrom "Arcade" beta is now live. In order to participate on the Arcade Beta, you will only need an active Battle.net account. Download the Beta client through your battle.net account and start playing some custom maps in this new platform.

The Patch 1.5.0 Beta introduces an entirely new Battle.net experience: the Arcade. The Arcade offers exciting new ways to find and play your favorite custom games -- and discover new favorites too -- with the option to search for games based on categories including genre, star ratings, release date, and more. After youve found a game that youre interested in, the new Game Info page will provide you with all the information you need to know before you dive in, including a description, screenshots, instructions, patch notes, tutorials, as well as star ratings and reviews provided by your fellow players. The Open Games list will help keep wait times down by displaying games that are waiting for players too.

Blizzard will support their mapping and modding community through "Arcade" which will improve the distribution of custom games in StarCraft 2.

Source:
Battle.net - The Patch 1.5.0 Arcade Beta Has Begun
Battle.net - Arcade Beta Forums