I also forgot to mention that nations at war with you (excluding Islamic ones) will not attack any of your units or settlements while you are on the crusade. Big plus if you're on the receiving end. But Venice might be dumb enough to do that so watch out. >.>
Not true. As England i got backstabbed by a France whom i had marriage alliance with as soon as i moved on my crusade. Even if France was wholely envelopped by my territories and was four times smaller. So no, being on a Crusade doesn't mean jack sh*t to the AI, except that it sees your armies marching away from your lands.