All points are covered in this thread, may i add it is essential to keep up to date with Google webmaster website guidelines information, follow Matt Cutts blog,interviews (on various sites inc WPN). This latter advice does provoke lots of controversey,but we do learn heaps from it.
Remember for PR Google ranks pages not websites..

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I climb high mountains,dive deep seas. I ride wild horses and fight enemies. When not doing all those things i sit quietly with a nice cup of tea.