I wrote a novel during Nanowrimo this year, and I've been using OpenOffice Writer to format the text into a nice looking book layout. I've previously been a Word 2003 user for about five years, and I have to say that I really don't find anything problematic with the transition.
I've got Writer on an Eee 1005HA-V with 2GB of RAM and it seems to load acceptibly quickly, and whilst the interface is a little different to Word 2003, there's nothing particularly missing or broken that I've encountered as yet: some features are actually better (multipage zoom out, for instance). Doing nice looking book layout is about the same level of hassle that it is in Word, and it seems to perform around about as fast for the task. When I run Writer on my quad-core desktop it screams along doubleplusfine.
On the basis of my experience, I'm really left kinda skeptical at the level of bad experience other people report with Writer. I previously tried OO version 2.x and discovered it sucked rather radically, but version 3+ seems a perfectly useable tool. Perhaps when I get to writing a technical document or textbook in Writer, I'll bump into problems, but I just don't see it for now.
I messed around with versions of Word past 2003 a few times in various workplaces, but none of them ever provided any functionality I really needed, and just shuffled the other stuff around in the interface to irritating effect.
Given these thoughts, I think Microsoft should certainly be worried: I'll probably never install Word again.