I went to a Best Buy store and tried Android tablets but didn't see any Leaderboard for Angry Birds Space edition -- is it because it is not logged in as a game user or does Android have a standardized Leaderboard similar to iOS's GameCenter yet?
Android as a platform doesn't have any equivalent to GameCenter currently. Some Android games use OpenFeint for leaderboards and achievements, but it's not an official standard of any kind and it's not implemented in the Angry Birds games specifically. Other games choose to implement their own leaderboard systems (PewPew does this, for example).
There are a few other options out there such as Swarm (aka SwarmConnect) that have similar functionality (leaderboards, achievements, etc.) for Android games. On Android it often comes down to developer preference.
Rovio now offers Rovio Account for their games on iOS and Android.
They describe it thus:
Rovio Account lets you store your game progress and continue playing on another device.
This is not related to the just-announced Google Play Games, which is a general platform for Android.