I don't want to challenge Suzanne's remarks, only offer my own version.
I would say that AutoComplete still works, but it doesn't work exactly like
it used to. I have defiined my full name as an AutoText entry. I type "G"
and press F3 and my fullname is "auotcompleted" in the document. What
doesn't work because it is no longer available is the "Show AutoComplete
Suggestions." If it did, I would have to type "Greg" and then enter.
In my opinion the F3 method is just as good as "Show Auto Complete
Suggestions."
I think the addition of "Quick Parts" on the Word Insert menu was a huge
mistake. The label is very misleading. Quick Parts is one of 35 gallery
types in the new Building Blocks collection in Word2007. Custom Quick Parts
is another, so is AutoText and Custom AutoText. The Quick Parts controls
has button control named "Fields" that opens the Insert Fields dialog.
Fields are fields. They may be part of a document, but they are certainly
not "Quick." Same goes for Document Properties :-(
There are 15 built-in building block galleries (the other 20 are custom
galleries). 14 of these galleries have a control dispersed somewhere on the
ribbon (e.g., Cover pages, Headers, Footers, Page Numbers, etc) where you
can click and see what the buidling block is and then insert it in your
document. The "Quick Parts" gallery is on the "Quick Parts" menu. No
surprise there, but you want see any if you haven't defined any. For some
inexplicable reason the Microsoft engineers left the AutoText gallery off
the ribbon. I think that is why a lot of people think that AutoText is dead
in Word2007.
I really isn't. All of the 35 galleries can contain a practically unlimited
number of categories and individual entries. With the partial and full page
previews you can quickly see what you want in the gallery if you can't
remember its name.
I put together an AddIn that adds the AutoText gallery (and the other 20
custom galleries) to the ribbon with some enhanced tools for managing
building blocks. You can review and download it here.
http://gregmaxey.mvps.org/Word2007_Building_Blocks_&_AutoText.htm
As for going back to your older version, why not keep both? Both versions
can run in harmony with each other.