Sgt_Kickaxe - 9:32 am on Aug 21, 2010 (gmt 0)
Definitely nofollow ALL affiliate links as well as all links to any redirect that leads to an affiliate site.
Take it one step further and reduce the number of such links to give your natural internal link structure some breathing room (ie: a bigger share of the rank flow).
eBay for example is requiring affiliates to use a 301 redirect and not a 302 redirect under threat of banning affiliates because they know the link juice flows to them via 301 AND they don't want affiliates competing against them with their own content. None of their tools add a nofollow tag either so right out of the box your affiliate links need work. 302 is the default browser code on redirect unless 301 is specified.
After acquiring a few incoming links and seeing SOME traffic flow the most important on page factor, besides unique high quality content, is internal link structure. It can still be done without inc links and good content but it's harder to maintain rank that way in the long run.
Tedster, that 2006 patent was helpful, if the code was implemented as per the Google guidelines, but I'm afraid it's taken the same route all webmaster controlled "quality" signs have taken of late, it's no longer used. I haven't seen any ratings stars on natural serps in a while, except next to google's own content, maps and sponsored links, have you?
A newer factor that seems to be involved is just having regular folks visit your site and then, as they pass Google's armada of web beacons somewhere else, they report to Google that "hey, I checked out that site and stayed 2.2 minutes while looking at 8 pages... which is above norm when compared to similar sites so my vote is thumbs up". How's that for on page content importance, make it sticky and get traffic.
Also, it's important that these natural signals grow over time and come from more sources. increases in traffic, pageviews and return visitors all likely play a role in your serps rankings nowadays so I'll repeat - make it sticky, stickier than your competitors at least and increasingly so over time.
Matt Cutts recently said that moving forward it may be best to work on one or two sites instead of spreading yourself thin on a lot of sites, I have a hunch the above explains why. The "beacon sightings" you generate will be more potent if condensed on a smaller number of your sites.