How much Skyrim?

There seems to be some disagreement here and in other places on the "size" of Skyrim. Some people call it a huge and epic world, others point out that it is much smaller than a MMORPG. I've seen estimates of the time required to play the main quest to the end of about 30 hours, and completely playing through all side quests of 100 hours. Which isn't half bad for a modern single-player game, but doesn't compare well to thousands of hours of content of a MMORPG.

Furthermore if you play Skyrim at a typical MMORPG rate of over 20 hours per week, 100 hours per month, there is a good chance that the Skyrim buzz will be over in a month. The question "Skyrim or SWTOR" won't pose itself, because by the time SWTOR is out, Skyrim might already be yesterday's news.

What do you think about the size of Skyrim, it's replayability? How many months do you think you will play the game? How does it compare in size to a typical MMORPG?