Something I've found with cats is that you can't really designate an area for them to sleep in. You can put them there repeatedly and try to train them, but in the end most of the cats I've owned have chosen their own sleeping place, and most of the time that place is on my bed with me. I'm actually shocked that my girl, Scarlet, is able to sleep with me every night. I toss around so much and I've several times stretched out in the morning only to accidentally kick her. She never seems to mind though, and she always comes back to sleep there. It is her favorite place to sleep during the day, too. The only times she avoids it is when the dog jumps on on there wanting to annoy her. Her second favorite place is my desk chair at my computer, which she refuses to get out of unless I start sitting down on top of her.
Has your cat chosen your bed as their place? Do you let them or want them to sleep there, or did they just choose it of their own accord? If you don't let your cat sleep on your bed, what do you do to avoid them jumping up on there anyway?