Taking care of your 2.5 update request now (via support email box) and you'll have access to the native Mac version now too.
Btw, I wasn't saying that if you increased display resolution that the render view would not also increase to "100%", I was just saying it's not a solution, saving out your renders that way is just a bad idea. Better to resolve the underlying issue of why the Save button never appears. Hopefully the 2.5 version running natively under OS X will fix the problem. Be sure to let us know!
- Oshyan