I'm thinking now that I'll use jQuery validation methods from the start which can make the form more interactive and interesting. If the form validates within jQuery then I'll pass it to my php validation method. In this case, I'll use to php to re-validate the form under stricter criteria and employ a "honeypot" in php, an invisible field that usually only a bot would fill out.
Why not just use php validation, though, and echo jQuery from within my php? I suppose the answer would be that using only jQuery validation form start will be much faster and more "fun". Once the form validates and is ready to submit it's passed along to the php validation which is a bit slower but is secure.