The first thing that jumped out at me when reading the press release were these words:

As a result, certain compromises and customer disclosures will be a necessary part of translating between the two formats.

That, to me, seems to be the thrust of the whole press release: Yes, we're going to help you convert your documents to ODF - but why would you want to? It's an inferior format, and everything is going to break when you try.

The most other significant thing was the amount of work that is going to be required in order to use the converter. It's not going to be the case that Office can just open and save and work with ODF documents just as easily as it deals with so many other formats; rather, it seems that opening an ODF is going to result in it being convereted to OpenXML, any editing will be done on the OpenXML document - and if you want to save as ODF, you'll have to re-export, and lose formatting information along the way.

I was going to write more about this, but I think it's all summarised over at Computerworld very well, particularly in the quote from Pamela Jones titled "MS: OK. OK, we'll set up an "OS" project to build an ODF killer. Er, we mean translator." (although, now that I think about it, that title in itself is a pretty good summary):

Here's the choice it is trying to posit: You will have to download their ODF translator yourself and install it. Or, just stick with Microsoft's one-stop competing solution that is built in to their software offering. Considering Microsoft's monopoly position, and my mom's and most governments' typical technical skills, guess what Microsoft hopes moms and governments will choose? I see a plan in not building the ODF translator into Microsoft's software. So truly clever. It looks open. But it's marginalizing ODF. I think the press release might better have been titled, "Microsoft announces what it hopes will be its ODF killer."