I've been watching with interest to see how fellow Vimmers are coping with the migration to Mac OS X: Mavericks. It sounds like MacVim has minor build issues, but even Homebrew was struggling so don't rush to upgrade just yet.
- CGContextErase deprecation notice in Mavericks preview
- Full Screen does not work properly on 10.9 Mavericks
Given that MacVim's maintainer, Björn Winckler, doesn't have access to Mavericks, I'd hold off upgrading your main development machine if you're a MacVim user. Remember that you can install Mavericks onto its own partition or USB drive, so if you're desperate to try it out do that instead of replacing your main OS.