I spoiled co-op course 3, chamber 8 by foolishly listening to the developer commentary before playing through the level.
Not sure why I did that. Can only blame myself. (Although most of the co-op commentary was safe apart from for that one chamber.)
Also had a couple of chambers spoiled by being paired with some git who already knew the solution and just wanted to race through it, telling me exactly what to do and complaining if I didn't do it immediately.

But most of the players I met up with were great, and co-op Portal is fantastic.
I'll be playing through the DLC once my ADSL stops pooping itself every 10 minutes.
And IntergalacticWalrus, Wheatley is not funny for many of us who cannot forget being subjected to the same voice -- long before and long since -- in the patronising, stupid, pseudo-whacky and unfunny UK Barclays bank ads. I know Stephen Merchant has done some good stuff but those ads are all I can think of when I hear his voice, especially when he gives an *identical* delivery in the game.
Wheatley might be the best comedy character and acting ever made but some of us can smell the strong stench of Satan's pecker on his breath, and it ain't nice.
Even if he was great, he'd soon become non-great if you heard the same identical lines and jokes over and over and over again. Especially in levels where you're forced to sit around doing nothing while you wait for the game to play itself through unskipable set-pieces. (Or can you bypass them in Challenge Mode?)
The update seems to have made it so I cannot select a single-player chapter when starting a new game anymore (even outside of Challenge Mode), even though I've finished the SP game twice. Weird.