Hi seriocomic. To my understanding their is no 301 redirecting involved with domain mapping. Is that right?
It depends on the differences in the domain names.
There are some minor ranking elements to do with having the keyword in the domain.
Also, it has been stated by a Google employee (yet not proven) that each 301 redirect has a tiny degrading effect on the value of the back-link, so the full PageRank value isn’t conferred to the new URL.
All that being said, as long as the old links resolve and are redirected properly (using 301 header responses) to the new URL, you should be OK. Expect a small blip before things return to normal.