At the bottom of ABC's blurb about the Grey's numbers:
Please note: Based on last season ('07-08), "Grey's Anatomy" is the most recorded and played back program on all of TV, as the show gained +2.1 million viewers and grew by +1.1 rating points in Adults 18-49 (+13%) from its first reported Live + Same Day number to its Live + 7 Day number. With current DVR penetration nearing 28% this season, up from about 19% at the same point a year ago, "Grey's" will see even greater increases in viewership this season from the initially reported next-day overnight ratings to the final numbers including all DVR playback.
[TY - It's a shame there isn't really that much info about the Live+7 versus Live+SD numbers out there. I also found the following enlightening...]
Grey's represents TV's most-watched scripted series telecast since early-April (4/10/08 - CBS' "C.S.I.") and highest-rated among Adults 18-49 since the beginning of February (2/5/08 - Fox's "House" coming out of "American Idol").
[TY - I except CSI will be more viewed when it comes back in two weeks... but the A18-49 numbers won't touch the Grey's premiere.]