I express my sympathies for those poor souls who do not get to both DM and play.
Each has its own rewards. Dm'ing is the ultimate expression of creativity, for those who never get to write their own novel, it is the closest thing to doing so, and the work is shared with the players, so you never are quite sure what the outcome of your story is going to be. Playing, on the other hand, is truly fun to both act on and react to situations the DM introduces to you.
I am glad to be in a group which has several players willing to share these duties. There was a time when I mainly DM'ed - and while fun, you will experience both a stifling of creativity, and general burnout. Seeing someone else's style for a while will give you much input on what someone does better than you, and how you can learn from these people.
Heck, I've learned many techniques just listening to the other DM's on this board! (A certain Mr. Kulp's story hour, for one.)
...And I say to any player who reads this board and doesn't get the urge to DM at least one campaign, I have to say:
"Whassah mattah wit' you???"
