Actually, truth be told, Office 2008 is merely a native version of Office 2004 with features that were too time consuming to re-write removed. To be fair, MS did throw a new skin over it.
The day I see a Mac version of Office that's fully compatible with the Windows version and has an Outlook client will be the day I actually get excited for a Mac Office suite from MS.
Not having seen or used Office 2008 yet, I'll take your word for it.
As for having Outlook on the Mac, I could see that as a good thing, but the one downfall of Outlook is that it's missing some email compliancy such as multi-mode emails (sending both text and HTML in the same formatted message). Entourage supports this.
Granted, if you need an email client for corporate use, then Outlook is it. But I've grown to like Entourage and hoping that 2008 doesn't change all that much. Especially when it comes to synching my Treo 755p to it, which if it didn't work, that would be a deal breaker and have me start looking for another solution (Mail.app, Address Book, iCal).
Like Outlook, Entourage supports categories, which I've been using for 10+ years now. That was one of the perks of using it under Outlook then moving to Entourage.
As far as being compatible with Office for Windows, I've not had too many issues. Just about every Word and Excel file I moved/move over from Office 2003 has come in without a problem. Some minor formatting issues have cropped up here and there, but that's about it.
I've not used Office 2007 yet, so not sure on how the file formats work and all that.