I've heard women on the Tri boards say that they're worthless, or that nurses etc. dislike them.
I'm here to say it's not true! I had a specific birthplan, with my 4 most important points bolded for my second birth (DO NOT OFFER ME PAIN MEDS UNLESS I ASK...and a few others) and I got the birth I wanted. The first time I had a more general one, and had pain meds forced on me.
Keep it to one page
Bold the important stuff
Realize a few things might change
Make sure to include HOW you want to labor (this was my one mistake last time, and in the heat of the moment, pushing on all 4s was abandoned. I was recommened a position (squatting) that was totally uncomfortable for me, but didn't have the energy to speak up. This is the one change I'll make this time.)