From my personal experience, after my first clitoral orgasm the sensitivity has increased a great deal, and in order to achieve a second one orally, the pressure of his tongue on my clit has to be much lighter. It also helps a great deal if he leads me up to it by licking around my clit rather than directly on the bud.

My master usually satisfies his need to stay "down there" by licking me clean of my juices until he is sure that I am able to tolerate more clit stimulation. The distraction and pleasure of his licking everywhere other than my clit is usually enough to bring my arousal levels up enough to achieve further orgasms.

As far as damage goes, their is always the risk on desensitizing the nerves due to too much stimulation. This is a real problem, and requires a great deal of time and abstinance from any clit stimuation to overcome it. The biggest concern would be the permanent inability to orgasm which would be devastating for anyone.