1 external monitor: for me, it hard locks 10.10 regularly -- no core, nothing in console, just hard lock. This was on completely stock brand new macbook pros.

2 external monitors: even worse. I quit trying.

btw, I love divvy [1] (best $13 I've spent in years). For those who don't know, it allows keyboard chords to move windows. Unfortunately, it doesn't have good multi-monitor support -- it moves windows only within they monitor they are on. That said, it's crucial for good typists. A typical use case: code in one window, docs in another. Use the keyboard to increase the size of the docs window so you can read it better, then shrink it back and put it back into the lower right corner of your monitor. It's awesome.

[1] http://mizage.com/divvy/

For the hard lock issue, check to see if the cpu is grinding to 200%+ utilization, especially spending most of the cpu on the kernel_task process. If it is, see if [1] will help. The tl;dr of that page is when the Mac laptops sense a high temperature, the quick and dirty fix Apple has in place is push kernel_task to eat up as much cpu as possible to slow down everything else enough to cool down the laptop.

I pointed my room air conditioner's vent directly against the bottom of my Mac laptop, and it happily drives my external monitors. Enclosure Bottomside temperature reads 18-20 degrees C, and CPU A Temperature Diode reads 60 degrees C while I'm cooling my laptop like this.

I agree with the great-grandparent's sentiment that the product polish for high-end Apple laptop products is definitely gone. It isn't that no one within Apple is unaware of these issues, it is too few are in a position to take actionable measures about these issues. The margin between picking a MacBook Pro and a high-end Dell/HP/Lenovo/System76 is as slim to me as back during the latter stages of the PowerBook days, the last time I switched back to non-Apple laptops for a few years.

Product marketing-wise, Cook is in a tough position that I don't envy. Apple is so big right now that every product revision has to support that "big", "successful" narrative, and he's getting painted into a corner to not jeopardize that story. This pushes severe compromises into product design decisions to go after the bulk of that bigness, and niches like influencer demographics get squashed in the process.

[1] http://www.rdoxenham.com/?p=259&cpage=2

"What's wrong with Apple's multi-monitor support?"

One thing immediately comes to mind: configure a multiple (3 or 4) monitor setup (again, not exactly exotic) and then full screen a video in one of the monitors ... now change focus to a different window in a different physical screen. Fun ensues. Different fun, depending on OSX release.

USB or bluetooth tethering is great - I'd prefer to use that always - but some use-cases demand a physical thing stuck into the laptop and the plain old USB A-type is flexibility I don't like to see deprecated. I'll gladly take 1mm additional laptop thickness in order to retain those and I think the 11" macbook air, with one type-A on each side, is a pretty powerful swiss army knife.

I'm not sure why you indicate 3-4 monitors is not exactly exotic. Pretty sure its the 1% or less. Wouldn't that be the definition of exotic?

Wait'll you see what happens when you rotate them!

We are living in a bubble, our use case is not even remotely close to the average or above average use case. Looking at the data broadly, this barely registers as a 'thing'.

Spoken as a multi monitor user too.

Is this including the mac itself (so 2 external screens)? Because I have that setup at work with a mid-2014 Macbook Pro and with the last 3 versions of OS X and everything works fine - video fullscreen while browsing on another screen is not a problem.