The Guestbook.

Options: A variation on the fingerprint tree (no messy ink required), slice of tree, small notes/evelopes in scrapbook, or photo/polaroid guestbook.

The Wording.

Might want some kind of sign telling people to 'leaf' their name or something of the sort.

The Placement.

How will the guestbook table be arranged?  Will anything accompany it?  What kind of pens?  Will it share the table with the gift table? The place cards?