That's actually a good question. I watch a limited number of shows, and I wonder if simply buying the DVD's of a program would turn out to be cheaper than actually subscribing.
Edit: I mean I've seen boxsets in BestBuy for as little as $25 and they're shows I watch.
If I had all the series of Simpsons, Futurama, Mythbusters, Family Guy and American Dad I believe from then on I believe I would rather use the monthly subscription fee (about $150 here for all the channels we want; TMN is great to have as they're free of charge for a monthly fee, I get all the recent Stargate and Dexter episodes and most of the big movies not too long after they're out for rental) for buying more boxsets and movie rentals.