Spanking - spanking, not hitting - doesn't really qualify as 'child abuse', but as a parent I can't say it's particularly helpful, either. I can't say I haven't used it when I'm at my wits' end. After you've tried rewarding good behaviour, witholding rewards for bad behaviour, and punishing bad behaviour with loss of priveleges, what else is there? However, my elder daughter, at least, just considered a spanking (or whatever punishment we gave, yelling, taking things away) as the cost of doing business. She got to do what she wanted and she paid for it by taking whatever we dished out.
So while I have spanked or slapped my children I can't say I approve of it as a useful method of parenting. It doesn't really help them understand why what they're doing is wrong.