Do they go w/the book title or the ISBN#?  I resisted tagging at first. But I can see the benefit of tagging my reminder list when I'm checking out deals on the bazaar board.  Since I have to look at everyone's elses tags for now they can look at mine too. But do I need to tag every version or does it go w/the title?

They must go with the ISBN #. There are tags on my bookshelf that I've never put there!

Well you can see other peoples tags.  Eventually the most common ones that pertain to every one will push out the tags like "my RL" .  You'll only see "fantasy" or "historical fiction" type tags.  My question is do I need to tag every possible ISBN# out there for a book. Or if I tag one version will it go w/the title and author.  Some books have several paperback versions w/a dif ISBN# for each one.

The Help Center says:

Those tags may be completely irrelevant to the particular copy of the book YOU will be requesting if you click "Order This Book"

I take it that it follows the ISBN.

Here is a book that has several different tags for the various bindings. Even when the is more than one type (HC or PB) if the ISBN is different the tag is not applied.

http://www.paperbackswap.com/book/browse.php?t=t&a=p