Here's a FAQ from BioWare:
How much is the Extended Cut?
The Extended Cut is available to download at no additional charge.
When does the Extended Cut release?
The Extended Cut will release on June 26th on Xbox 360, PC, and PlayStation 3 in North America and July 4th for PlayStation 3 in Europe.
How large is the Extended Cut?
The Extended Cut requires roughly 1.9 gigabytes of storage.
How do I get the Extended Cut?
The Extended Cut can be downloaded from Xbox LIVE, Origin on PC, and PlayStation Network at no additional cost.
What is included in the Extended Cut?
The Extended Cut expands on the endings of Mass Effect 3 through additional scenes and epilogue sequences. It provides more of the answers and closure that players have been asking for. It gives a sense of what the future holds as a result of the decisions made throughout the series. And it shows greater detail in the successes or failures based on how players achieved their endings.
http://masseffect.bioware.com/about/extended_cut/
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the dreamer of improbable dreams