It has been discussed before, but that's because it's such a big and common subject. I have a 19-month-old who is also 'rough' (that's the euphemism I find myself using) yet has a very affectionate side. I have posted here myself about this very problem. I can pass on advice that has been given to me but I find that it is a very persistent problem. I agree that it seems to increase along with disruptions/changes in my son's life. It may be the only way he can express anxiety/worry he is feeling. It is also related to my son's inability to speak, I've been told, though I don't know at 2.5 years if that is so much the case. I've read in many places that in general, kids this age sometimes just are this way, not having the inner means to control themselves yet. I find I have to deal with feeling resentful about the physical pain. My ds pulls hair VERY hard and scratches and grabs faces. It really hurts, and he has to be watched very carefully around other kids. I have to snatch him away from another kid alot and I think he picks up on my anxious hovering when he's around another kid and it makes it worse though I can't not do it. What has worked best is this: when he does this to me I put him away from me, firmly but without giving in to being angry and punishing. I say something like: "Ouch, that hurt. I don't want to play with you when you're like this." Usually he's unhappy about this, so after a beat or two I pick him up again and give him a cuddle. Of all things, this seems to work best in terms of stopping a total frenzy of biting, hair-pulling, etc.
In conclusion all I can say is: I sympathize because I know what it's like and it's hard. I wish often that he was the kind of kid that just didn't do this. I recently read The Successful Child by Martha and Dr. Sears and got depressed. I feel like I did all the right things and yet ds is so often hurtful. Occasionally I just hate the situation with all my heart. I keep telling myself that he will eventually outgrow it, that kids at this age simply do not have much control over their own actions or the awareness that their behaviour is hurtful. I know that it'll sink in eventually but in the meantime it is the hardest thing of all that I have experienced as a parent. I told this to our pediatrician and she recommend Occupational Therapy, to jumpstart talking which in turn should lessen the aggressive behaviour. This is just getting underway so I can't say whether or not it is helping. But that's how bad it is: my husband and I got to the point at which we felt we had to do something as major as this. So I want you to know, I take a post like this from another parent VERY seriously.