my Master practices orgasm deprivation on me (see a post in the 'My BDSM Life' section) i think the key is probably knowing someone really well in terms of what they like and their repsonses to things and, of course signs that they are close to orgasm etc (in my case usually begging very loudly - unless i'm gagged of course). i reckon it's the same for having many orgasms, if the scene is good and you know someone enough to know their body etc then this should happen over time.

Hope this is of some help.

sl