Been thinking about this as the final season approaches. Please know this is all for curiosity's sake. I am somewhat ignorant on how ratings are currently tabulated anyway. And I'll be watching the finale (and season) no matter who else is(n't).

Anyway, below is a link to a Wikipedia list (using Reuters, Variety, Nielsen Media Research, and ratings data from USA Today) of the most-watched series finales of all time.
http://en.wikipedia.org/wiki/List_of_most-watched_television_episodes#Most-watched_series_finales

121.6 million viewers tuned in for the M*A*S*H finale.
93.1 million viewers tuned in for the Cheers finale.
76.3 million viewers tuned in for the Seinfeld finale.

It's interesting, looking at the ratings averages across seasons (from Wikipedia, I know, I know, but they're source-cited), they seem pretty comparable to that of LOST's.
M*A*S*H - http://en.wikipedia.org/wiki/M*A*S*H_(TV_series)#Season_ratings
Cheers - http://en.wikipedia.org/wiki/Cheers#Ratings
Seinfeld - http://en.wikipedia.org/wiki/Seinfeld#Ratings_history
LOST - http://en.wikipedia.org/wiki/LOST#Ratings

Like LOST, the other three shows had massive fanbases, somewhat comparable ratings across seasons, and became pop culture phenomen(ons/a). But how big is LOST, really? As a fan, I'm biased, of course, and think the show's a massive success. But will that translate to high viewership for the finale? And in light of all the modern avenues for watching TV, does it even stand a chance at receiving high viewership?

We know the diehard LOST fans will show up and the casual LOST viewer is bound to tune in.

But will the finale draw folks who stopped watching LOST seasons ago for whatever reason?

Will it draw folks who are curious to see what all the hoopla has been about all this time?

What about folks who just watch series finales (do they exist)?

Or, since the show falls under the mystery genre, folks who like to be spoiled or to "read the end of books"? Not that mysteries won't be revealed (I assume) throughout season 6.

And let's not forget the TiVo/DVR/Hulu/online crowd - I assume those numbers count also?

So, what say you?

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P.S. Interestingly enough, according to that Wikipedia link, the ALF series finale had more viewers than the ER series finale. Would've never guessed that and I'm a huge ALF fan - so no disrepect is meant there.