What percentage of PageRank is lost through a 301 redirect? [Google Webmaster Tools Video]
http://www.youtube.com/watch?v=Filv4pP-1nw
Short Answers:
1. Yes, it's beneficial if domain A has a historical backlink portfolio that has anchors related to the content of domain B.
1a. If the domain has a record of being dropped after relevant links were built to it, Google basically resets the "link meter" so any links discovered prior to the drop date are unlikely to count for anything.
1b. If the domain has dropped you may or may not see a benefit in 301ing it to domain B. I've seen rather mixed results with this. It is generally believed that less or no drops are better. Now, if it has been dropped it will probably not hurt you to 310 it, but don't expect it to help you much if at all either.
2. Yes, too many 301's are bad. I would say 1-3 are safe, 4-6 moderately safe, 7-10 probably pushing it.
2a. The above statement does not include URL shorteners like bit.ly and TINY-URL (remove dash) HOWEVER keep in mind that if the majority of your links are coming via 301 domains or 301 shortened links it will raise flags.
3. In my experience I estimated approx. 90% of PR is passed so long as the domain hasn't dropped and points to a site with them same theme as it's backlinks prior to the redirection.
4. Reasonable justification:
a. You notify Google of a domain change via web master tools
b. Site overall themes match up
c. Both sites are consistantly linked to over time prior to the 301ing of domain A
d. There should not be an immediate drop off of links on Domain A, slowly transition away from it and focus on domain B... OR try to keep a reasonable balance between the two.
e. The domains are similar in nature, such as a small type, similar keywords, etc.
5. I have noticed a some what diminishing effect in 310 domains (I am still assessing this factor), so while I believe it is still a valuable technique to use, I advise to not over abuse it as mentioned in #2 and #2a.
