I'm going to disagree with a lot of people in this thread. A lot of aikido techniques, even when done properly, do inflict pain on the uke. That is not to say that goal of the nage ought to be to inflict pain, but I would think there is something wrong if I spent half-an-hour practicing sankyo and felt no pain at the end of it.
I doubt we disagree very much. I don't expect aikido practice to be painless. Most of the people I know practice very hard and the wear and tear adds up. But generally its pretty obvious when someone is adding in an unneeded crank or slam or ignoring a tap out.