i've done it three times. it's like what you've said... follow the bride all day. IF she sits all day, you sit with her all day. If she helps with preparation for the dinner, you help. If she goes to pee, you have to stand by the door. If you need to pee, you have to tell her to wait for you. Of course, you also get to do some drinking... just be smart when they try to give you drinks.. always make sure you give them the drink they give you back so you won't get drunk. meaning if there are two cups, you drink one and make them drink the other one.
It is very very very boring, but then... they do give you money too at the end of the day. Have fun!