Yeah, the papers I've read on the subject have difficulty establishing a definition for shamanism and it seems there's no consensus. The only definitive aspect that I'm aware of is the use of altered states of consciousness to acquire knowledge.
I haven't heard of Frazer's text, but will pick it up when I can. Shamanism is a new field for me; I recently stumbled upon it as an area of formal inquiry while looking up the lore behind World of Warcraft's class by the same name, which led me to Wikipedia, which led me to Eliade's Shamanism: Archaic Techniques of Ecstacy as an authoritative source of information. I've only read the first 200 pages (up to costumes & rituals), but am really interested in:
-the "initiatory madness" period of shamanic induction,
-the idea of wounded healing,
-the mythological shaman figure as healer, spiritual leader, and magical interventionist, and
-the use of ASC's to achieve insight and transformation.
The crossing of boundaries is interesting, too - it reminds me of your posts about the psychopomp. In some ways, this aspect of the shaman strikes me as akin to the tendency of Ni-doms, particularly INFJs, to pursue a quest for insight and personal transformation, the fruits of which they bring back from the Beyond to share with and heal their communities. I don't know if that's a genuine relationship, but it struck me as I was reading Eliade's book.