I've had great success with the old 1.6.1 edition of the Arduino IDE that was offered via Github and decided to try upgrading to 1.6.4 and installing the board as per the instructions. I have encountered the following three problems:
1) My one macbook (MBP 2012) cannot upload code to the ESP8266 at all. Error is consistently:
error: setattr stage 1 failed
error: espcomm_open failed
I've verified that I have the correct drivers for my USB to serial cable and can select the appropriate device from the Tools->Ports dropdown. It was working fine under 1.6.1.
2) Compiling sometimes hangs and restarting the app does not clear the issue. After ~5 minutes it seems to clear.
3) Uploading is intermittent, sometimes it works and sometimes it doesn't. Sometimes it dies mid-upload and other times it has problems connecting. In 1.6.1 this was rock solid. At the moment my larger sketch uploads however the ESP8266 continually restarts and I'm not getting any of my debug logging coming out. This sketch was working fine in 1.6.1 and still compiles fine in 1.6.4.
Overall I'm rather excited by being back to the mainline Arduino.app, however the current roadblocks mean that I'm going to revert back to using 1.6.1. I had migrated over because I needed use of the F() macro and instead will be backporting it for my project.
Thanks for all your hard work!