I would think that a "gentle" spanking would be annoying.
One solid masculine pop, with some force behind it, seems like that might be what would be interesting, at least to me. Then gauge the reaction and go forward with more, lighter or heavier.
Of course, you might get smacked if it's someone else.
There is a GREAT topic concerning spanking in the forum "Another Realm". I would ask the lady that you're interested in seeing and then judge what to do from there. In the heat of the moment, a little spank here and there (along with some hair pulling) ... is fantastic.
Here's a link to the topic that I mentioned:
http://www.eccie.net/showthread.php?t=65052
Elisabeth