The good news is that Novell has promised that it will release code for OpenOffice that will support the new file format, but it'll be at least another month or two before that's a viable option for end users, and there are still many corporate users who will be stuck since many of them don't have the option to use or install OpenOffice. Also, just because Novell releases the code to the open-source community, it doesn't mean it will actually get integrated into the OpenOffice suite, although it's a good bet.
Windows users with Office 2003 will, of course, be able to download a compatibility pack that will let them open Office 2007 files, but Mac users are being left in the cold, probably for months, while the Mac Business Unit at Microsoft takes their time in making a similar solution available to Mac users.
I know the comment section will now be flooded with comments about how Mac users should ditch Office completely and use OpenOffice, NeoOffice, ThinkFree, iWork or a host of other Office alternatives, and that's fine and dandy for many people. I encourage people who have the choice to explore other options on their personal or work computers that aren't completely locked down, to do so, with gusto. But the fact remains that the majority of corporate IT departments don't see it that way and since many of them still resent having to support Macs to begin with, these compatibility issues just make matters worse for Mac users in those environments and it makes it that much harder for them to do their jobs.