I have been having nipple orgasms since I was nineteen and over several decades have made all kinds of discoveries about the orgasmic potential of the nipple.
There are two things that make nipple play my preferred form of solo sex. First. after a nipple orgasm there is no refractory period. That means you don't have to "recover" from an orgasm before you can have another. This means you can have multiple orgasms within a short span of time. I have had as many as a dozen orgasms in a half-hour period. Normally in a nipple orgasm session I have a cluster of orgasms, usually three or four, but often more.
Second, stimulating the nipples turns your entire body into an erogenous zone. When you get close to an orgasm by nipple play, or just after you have a nipple orgasm, it is possible to orgasm by massaging almost any part of your body, and these orgasms are just as intense, sometimes even more intense, than the nipple orgasm itself. As long-time members of this group know, I regularly have breast and belly orgasms, usually in combination with nipple orgasms. Just a few days ago I brought myself close to orgasm by nipple play until my whole body was humming
in sexual ecstasy. Rather than climaxing with nipple play, I began vigorously rubbing the underside of my thighs, and had two powerful orgasms, back-to-back, in this way.
If you want to know more about nipple orgasm, I have a Yahoo group dedicated to the topic:
http://groups.yahoo.com/group/nipple_orgasm/