820,000 unique participants contributed to over 12 million hours of online gameplay, which averages to 14.6 hours per person. According to the press release, that number is "equivalent to more than 1,400 years of continuous play by one person," but since one person cannot play multiplayer by themselves, we're going to rephrase that to "a 700-year long death match." Somebody tell the Highlander.
With approximately 8,760 hours in one year, a 1,400-year game session would put the total play time closer to 12.26 million. 260,000 extra hours is nothing to scoff at.
The press release also claims 350 terabytes of data downloaded from Xbox Live. At 1,000 GB per TB and approximately 900 MB per Halo 3 beta, that amounts to just under 390,000 downloads. That equates to approximately 2.10 unique participants for every download. Xbox Live servers therefore would have sent out all data from the Library of Congress five times.
Finally, 580,000 saved films created by users, representing more than 2.7 TB of data and amounting to around 1.49 films per download (or 0.71 per person). Got all that? Good, keep studying because you'll all be quizzed on it later.