I don't have one, but am still trying to decide if I should get one for ds for our next trip. From what I remember, the new one costs about $65 (they don't offer the daily rental anymore..I don't think). You can try to get the older version off of e-bay, etc., but I have had no luck finding one for less than $40 plus shipping.
He's gotten a lot of mixed reviews. Some people love him, and have gotten tons of valuable information using him. Others complain about not being able to hear him and that it's a pain carrying him around all day...and end up leaving him in the rooms.
If you do a search here, I'm sure you'll find tons of threads with the various opinions.
I have a while before I have to decide. I'd hate to spend that much money if my ds won't really use it.