This morning when I checked my account, I have a wish list 48-hour hold for a book that shows 3 copies in the system (reminder list).  Does this mean that 3 people have their books on a vacation hold?  But still my shelf is not on hold why didn't the book just go to the requester?  Curious.  Any thoughts?

My take on this is that someone had the book on their wishlist (not autorequest) and went on vacation hold.  In the meantime you posted your copy as did 2 other people.  When the account came off hold, your copy was offered to them and they have the regular 48 hours to respond.

Sounds like your book has been offered to a requesting member.  Are you sure your copy is #3?  It could have worked it's way to #1, or (as you mentioned) the other available copies could belong to members on vacation hold.  Or, the book could have been requested directly from your bookshelf (but IIRC those have the 1 hr. Buyers Remorse period, not the 48 hr. hold).

The book is on 48 hour hold because the requester does not have it on auto-request, the system is waiting to see if the requester has credits and still wants the book. 

The person's wish was on Hold when the available copies were posted. Now they've taken the wish off of Hold and your copy has went into a Wish List hold for them to confirm they still want it.

I have a few books on Hold on my Wish List that have since become available. I think this will be a more frequent occurance since they made the individual Hold on the Wish List available.