Sunday's Lost finale was a "television event", but how big a "ratings event" will it be?
I'd be surprised if it came close to its series viewership highs from past seasons. If that Wikipedia linked chart is correct, its second season premiere was over 23 million viewers. That's almost twice any episode so far this season.
I wouldn't be surprised to see its highest viewership and 18-49 ratings for this season, but I don't think that series highs are in any danger of falling.
For reference, this season's Lost premiere episode averaged 12.09 million viewers (Live+Same Day), and the most recent Tuesday episode (5/18) averaged 10.47 million viewers. While I don't have a nice chart of this season's viewership, you can see Lost's new episode 18-49 ratings below.
What's your guess?
Note that the dates in the chart above are for the Sunday following the episode airdate.