In my professional opinion ... er, what Andy Collins and Will said.
Honestly, the 3.5 books are solid. No one can guarantee that they won't include the occasional typo and awkward sentence (I've noticed a
very few here and there). That written, remember that the WotC folks have been at these revised versions for about a year now, and they've enjoyed (

) the benefits of all the comments and critiques of those publishers given access to drafts of the 3 core books.
The writing's been cleaned up and clarified, the organization of the books (especially the DMG and the MM) has been rethought, and the overall attention to detail has been intensified. Very often on the top secret revision mailing list, the WotC folks had already caught and attended to stuff that publishers brought to their notice (they also looked carefully into addressing whatever issued they had not already covered.)
You will, of course, need to decide for yourself by looking through the books. Yet, as I wrote earlier in this thread, I think you'll be pleasantly surprised.
Take care,
Mike
P.S. I'd just like to thank Duke Frinn for posting those comments from Andy Collins. Mr. Collins is dead on right, I think (though perhaps editors of science and math books also have it tough

). Editing game books well, particularly d20 books as the system itself is rather intricate and complex, really is a special kind of skill. I've needed three years to understand that fully, and I still have a ways to go .... ("Salad Lord," anyone? [NOTE: See
The Tome of Horrors.])