I expect that a number of issues affecting playability will remain open after 1.9 is released, regardless of whether the 29th is the actual release date. I see some growing frustration on the bug tracker regarding specific issues, consequently. Which issues you consider to be game-killers probably depends on your playing style. For MP, performance issues are probably of the highest priority. I'm more interested in some of the technical details that are either broken or ambiguous.

What would cause you to postpone upgrading to 1.9?