Here is the complete post from IceFrog's blog:
DotA has come a long way in the past year. With more and more users playing and providing feedback every day, I'm sure that 2009 will be another good year for DotA. One of the things I will focus on this year will be improving the quality of existing content. I will certainly still be adding new content, but I will also spend more effort to make the current game play experiences more enjoyable for all.
I have been working hard on 6.58 and was hoping to complete it for New Year's Day, but I don't think I will be able to finish it in time. There are still some issues that need further testing. I want to make sure the quality is high, so I think I will need at least a few more days to work on it. This update will have some frequently requested hero and item remakes, balance improvements, some bug fixes and more. I have also spent a lot of time on core code rewrites for further performance improvements so that players with older machines can also fully enjoy the game.
If there is anything specific you want me to make sure I address before 6.58 is released, let me know. Once I get this update released, I will probably be able to do a little more blogging and another round of Q&A.
Source: http://www.icefrog.com/content/happy-new-year