I never heard of the dollar dance until I saw it described on alt.wedding - I lurked there when I was planning my wedding a few years ago.
IMO, it's tacky, because it constitutes asking for money/gifts. The bride and groom and their families should not give the appearance of asking for money or gifts. It's one of those weird unwritten rules... you can't give the appearance of asking for a gift, yet your guests "know" they should give one. No, it doesn't make sense.
