I had postponed upgrading to Yosemite because of all the horror stories about 24-hour delays while the installation program copied all homebrew files from /usr/local to hell and back, and things running slowly afterwards, and, well, what always happens when you upgrade.
But I am progressive by nature and there were several things I wanted to install that required Yosemite and that was going to be a thing too. My great surprise was first that perhaps because I have a solid state drive on my MacBook Air, there was a delay, but not that much. And secondly, everything was snappy as all getout after the upgrade. I felt like I had a new computer running!
MacVim has long been my standard Mac text editor, and gvim on Linux, although now Atom with the vim mode and markdown plugins is vying for that position (make sure it's always running to avoid delays in loading), along with LightPaper for Mac for markdown. Imagine my chagrin when I attempted to open a text file on Yosemite with MacVim, only to find that while the application launched, the window didn't. No go.
This article explains what I did to remedy the situation completely on my MacBook and bring MacVim back to the contender status it deserves.