We started signing with both of our boys early on and saw no delay in
their language. If anything, we think it helped them. The key is to
make sure you are always saying the sign when you make it and to
introduce them one at a time. We started making the signs to them at
around 6 months. We started with More, Drink, Eat and Milk. Next, we
taught Help, Yes, No, Mom, Dad, Dog, Please, and Thank You. We taught
ASL instead of making up our own signs. It just didn't seem to make
sense to make up something that no one else would understand. We
found that we ran into a lot of people that knew even just a little
bit of ASL.

As they got older, teaching sign language was more of a novelty than a
tool, but they were still interested, so we created a calendar to
teach them a sign a day. Usually we had a theme each week – fruits,
weather, the next holiday, etc. The calendar included the printed
word and a picture, so we used it as a reading/spelling/vocabulary
tool as well. We slacked off after awhile, but with baby #3 on the
way, we're planning to pick it up again. Our oldest often brings just
his hands to show-n-tell and teaches the class some signs.

We have given signing books to several friends as baby shower gifts
and they have really loved them. Our favorite is "Sign With Your
Baby", by Joseph Garcia. http://www.sign2me.com/default6.htm. There
are also some websites that have QuickTime videos of the signs which
is a great way to really see what it is supposed to look like. Try
http://commtechlab.msu.edu/sites/aslweb/browser.htm

I agree with the comment about being a great tool for communicating in
public. The "toilet" sign is especially handy in church when you'd
rather they not announce their need to go to the whole congregation.
It also works well across a crowded room.

Good luck!

~ Sher, due with boy #3 9/27/03