Yes, you need to tape the seams. It's needed for when the house moves.

This post was edited by snookums2 on Tue, Apr 2, 13 at 14:00

Are you using Hydroban?

If so, read the Hydroban instructions. If you do a neat job installing your cement board, you can treat/fill the cement board seams with HB, then once that treatment has dried, you can do your full-coverage coats.

I highly encourage you to read the PDF on Laticrete's website.

If you do go the alkali tape and thinset route to treat the panel seams, do not create speedbumps. Remember, this isn't drywall. You're simply looking to tape the seam and fill the gap with thinset. You want the face of the board to be dead flat. No Speedbumps!

Good luck!