I could see Microsoft getting in trouble if they were "changing" PDF's, yeah. But if all they were doing is outputting/editing, then yeah, there are tons of other programs and utilities that do the same thing.
They are outputting only, Office 2007 cannot edit existing PDFs.
Which makes the whole thing a little silly. Adobe Acrobat (full version) still adds the extra value of editing/modifying PDFs, so I don't understand why they have a problem with their format being more widely available for users.
Plus, I've always hated the Adobe plugins, anyway. PDF reader always hangs my OS when I try to shut down if I've displayed a pdf in an IE browser window.
One more point:
The difference between a "fully integrated" save as PDF feature vs the "print to PDF" add-ons is that Microsoft's version actually maintained hyperlinks, bookmarks, tables of contents, all those handy things. Most of the other add-ons can't do that.
Ok, really my last point:
I don't know where people are coming up with the idea that Microsoft is "extending PDF" or "messing with the standard" or something like that. It is an Export-to-PDF feature that should result in 100% compatible PDF document. And frankly, from what I've seen, Office 2007 Beta 2 puts out some of the cleanest, nicest looking PDF documents I've ever seen.