Performance with the latest developer preview of Yosemite has been verging on unusable IME, even dragging windows would lag substantially. The 'fix' for me was checking 'Reduce Transparency' in Accessibility. UI animations are now perfectly smooth. Hopefully the GM will mitigate this a bit, but I'm not expecting much improvement where transparency is concerned. The 1st Gen retina models are right at the edge of what is required to push a display of this resolution. So, just an FYI to others that might be complaining about performance in 2012 and earlier models.