I have a list of them (PR5-7), but I am worried that if I point more than a few directly to my site I will incur Google's "Unnatural Links Penalty".
How aggressively can I go for my PR1 site that is just over a year old?
I suspect that just as it is a bad idea to point a lot of crappy links back to your site, it is also bad to point too many extremely good links back to your site.
Furthermore, should I have no more than one link from each site to my site, or should I only be wary about more than one link from a particular site to an individual page on my site?
Would it be safer to just backlink my existing backlinks and get the indirect link juice back to my site?
And would Google penalise me if a whole lot of my existing backlinks suddenly jump in PR?
Finally, does Google analyse the backlinks to your backlinks? So would it be bad for me if a large proportion of my backlinks have backlinks from a only a relatively small number of sites that are in common with each other?