Don's arc this season seems to have him spiraling toward serious crisis.  He started the season enjoying at least a semblance of stability and order, it seemed cemented with the birth of baby Gene, but then began moving toward greater and greater risk taking, both professionally (the accelerating feud with Roger, hooking up with Connie) and personally (the stewardess, nearly taking on Gene, the incident with the hitchhikers, now the teacher).  Last season, his arc seemed to lead to the "big reveal", where the audience got a bit more insight into why Dick Whitman became Don Draper.  Is this year's arc leading to the "big crack-up"? 

Maybe Roger's words ("You're in over your head!") are prophetic.

I bet you're right, jk.  I keep thinking he will pull out of the agency and start his own.  So many did that.

He can't do that anymore. He's now under a 3 year contract, which I'm sure contains a non-compete clause.

I agree, he won't leave, and what a skillful way to keep his character in stasis.  Like with Joan, Duck, and now Sal, people move around a lot in business, but at least Don is staying put.  He's definitely heading for a crack-up, but I think the baby is the last straw, that's when he started to lose it- especially that whole weird hallucination (?) with the prison guard. I think that DD knows that he doesn't do well with obligation. I'm wondering what form his freak out will take!

I agree with Jack - I think from the outset of the series we as viewers have been primed to expect to see tragedy of Grecian dimensions. And it's not just Don - he only seems to be the most obvious barometer for the general healthlessness of all of the characters.
I also agree with mneeley that Don not only wouldn't but couldn't go out on his own and this inability to read what he is going to do and how he will ultimately end up is exactly what I love about this show.

Achilles
Julius Caesar
Pandora
All people who met with bad ends.
Gene having Sally read The Rise and Fall of the Roman Empire.

I think we're finally seeing this season's theme.

Interesting observation - it would be tied up with a bow if Achilles and Pandora were part of Roman mythology.

In any event, Gene's "All hell is going to break lose" seems more prophetic now.

But Don is similar to Achilles, and Pandora...well, the box.  There are lots of mythic/iconic themes here. My theory is that Don is not yet built up enough for an epic fall.  Maybe next season...