I've been using a Chromebook Pixel as my primary laptop for over a year now and have just gone back to using a Mac. (A 15" MacBook Pro to be exact.) The reason for retuning to the Mac was simple. After a hiatus from developing, I've been finding myself getting drawn back into writing code.
What I'll miss
1) Google Hangout Integration
With the Chromebook, Hangout is a first class citizen. It sits comfortably in the system tray at the bottom right of the screen and can be docked to the edge of the window to have a persistent presence. Given I work exclusively with distributed teams, this is possibly the most missed aspect of the Chromebook.
On the Mac, Hangout feels awkward in comparison. Maybe it has always been awkward - somehow Hangout doesn't feel like it really belongs on a Mac.
2) Google Drive as the file system
In Chrome OS, Google Drive is part of the file manager. It could be better as there is still a little awkwardness in the UI, but it still feels like it is part of the OS. My business is run using Google Apps so this is more valuable that it might at first appear.
On the Mac, I installed the Drive sync app which puts all your Drive files on the local file system and keeps them synced. On the whole then syncing works well. However I'm already finding myself putting files outside Drive - I know that this is down to me, but I never even had the option on Chromebook.
3) The Pixel screen
I was sceptical when I read the Pixel had a 3:2 screen to support better browsing. (A taller screen is more useful for vertically scrolling content like web pages and documents.) Now I'm back to a wide screen, I rather miss the retro screen size of the Pixel. Of course a 15" MBP has an excellent screen so I'm not suffering.
The Pixel screen quality is great, but doesn't set it apart from the MBP - at least not for me.
What I won't miss
1) Google Cloud Printing
I generally don't need to print much, but doing it from my Pixel was never a great experience. With Chromebooks printing is done via Google Cloud Print. My Cannon printer supported GCP - but that was sheer luck.
Cloud Print actually worked quite well however the printer itself was the problem in that it didn't seem to persist the cloud print settings if turned off - and my printer is mostly turned off. In addition, the printer could only be registered to one Google Account so I had to shuttle documents back and forth far too often.
In comparison Apple's printing support has always served me well.
2) Forced restarts
The Pixel (and maybe all Chromebooks) is 'always on' when in standby mode. This means there is always some battery use, if the laptop is closed but not shutdown.
Often I would find the Pixel had shut itself down overnight and I suspect it is in response to the battery getting too low.
Either way, a computer that shuts itself down without user interaction is a no-no.
3) The Keyboard
There is nothing wrong with the keyboard on the Pixel. It's actually very good.
But after a solid year of intense use, it's starting to creak. And I quite literally mean creak. Some of the keys make a strange squeaking sound.
This isn't too disturbing, but compared with the Pixel, the MBP keyboard is much better. It just feels more solid and satisfying to use.
4) Performance
Given the Pixel has 4GB of RAM, I was often left feeling disappointed with performance. And if the machine is left running for several days, performance degradation was noticeable.
Things you might expect would come up, but didn't
1) Offline Support
I don't find having a full blown laptop much of a benefit when offline primarily and this is because I'm wedded to Google Apps, email etc.
2) SSH / Remote Desktop
I have my Pixel in developer mode so I could easily create SSH connections. For remote desktop I used the xxx extension which works admirably.
So, support for these items isn't noticeably better on the Mac.