Just a quick one…
As we have known for some time a 301 redirect is treated by Google the same as a normal link and the PageRank/link juice/weight/whatever… flow is the same through both.
So when you need to do a 301 redirect, you don’t have to worry about more PageRank dissipating than for a normal link. So why did I underline need? Well although 301s don’t hurt you any more than a normal link, if you change your URL structure and you don’t really need to and then redirect the old URLs with a 301. You are losing PageRank when you don’t need to.
Remember part of the reason PageRank works in the way it does is that there is always a percentage of power that never gets transmitted via any link. Some say this is between 10% and 15%. However, it is always worth remembering that whatever the percentage the link will not be equal to all those on the page, so the actual loss is based upon that fact.