yes Read the google terms before you start they are very clear You can also put 1 search as well and 1 ref and 1 link Good Luck
I've seen in many sites having too much adsense units(more than 3), then it would be against Google's TOS?
Actually last time i try to put 4 ad unit, but no use. It will only show ad on 3 ad unit. Another one will be blank.
I believe 3 ad groups is largely sufficient. If you need to have more ads, you can use the larger banners.
I noticed that when I had more than 3 google ads per page it wouldn't display one of them, because of there TOS. I didn't know why it wasn't working, but I finally figured it out.
i have 4 refferals on my page and 3 ads ... is that bad? i asked my friend and says its okay ... just to be carefull with the ads one .. the refferal could be all 4 he said