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Holding events, writing blogs, publishing articles, etc. - basically putting useful information out there.  I've gotten most of my business from referral traffic, meaning traffic from people clicking the links I get on other websites.  So the links are the end to themselves, not just a means to getting promoted in the rankings.

I've found the ROI calculations built in to Adwords aren't always accurate.  Generally looking for the keywords with the higher quality scores (you will have lower CTCs on these) and those with good CTRs is a good place to start.

I find that the "short tail" highly competitive keywords are less profitable than keywords that are more specific or niche.

Btw google economists have published training videos on how to set your bid prices.  Basically you look at your revenue per keyword and then backtrack to determine how much you should spend.

Branding and visibility issues aside, from a pure link standpoint those links don't count (or shouldn't per Google).  Google wants affiliate links to be nofollow since they're advertorial (Matt Cutts on the matter - <a>http://www.youtube.com/watch?v=1SmlsfSqmOw</a>).  Cutts also says affiliate links should be disclosed adequately.  Now on the other hand, you're right that these links are benefiting a company that has these relationships set up.  I'm sure they're getting visibility, traffic, and ultimately sales.

Your first link didn't work.

Links from these shallow sites probably won't help much for passing link juice (low authority presumably) but if they're getting traffic then you might want those visitors to see your flagship brand where you have the bulk of your content.  In that case, it would benefit the visitor and therefore would be worth doing.

As always be careful with linking to your flag ship site if the shallow sites are linked to by spammy sites.  It seems to already doing pretty well so taking chances for minimal benefit probably wouldn't be worth it.

The blog link you mentioned will provide diminishing returns as the initial link you get from a domain is the most helpful and each subsequent link from the same domain is worth less and less.

The forum does indeed sound sketchy if there are links to unrelated sites.  You are in a good position because your competitors link profile doesn't look great.

I also look at the proportion of DA and PA to number of RDs.  The lower the ratio (more RDs) the worse the link profile is.  For instance a site that has a DA of 30 with 15 unique domains has a great ratio.  A site with DA 30 and 500 RDs has a much worse link profile.

This particular site is not impressive.

I agree with what's been said.  I think you want to be very wary and careful of link opportunities.  There's a lot of danger in these tactics and for $5 I couldn't imagine that the ways of obtaining the links would be anything but spammy.

Contrary to what a lot of people say, I don't think it's all that difficult to get quality links these days.  If you're marketing your business in all the other legitimate ways, natural and high-quality links will follow (no pun intended).

Eric, I'm really confused.  AddThis automatically adds a tracking code each time the page is loaded.  If you click refresh you'll notice that the code changes.

What do you mean the URL isn't being indexed?  Google is ranking that page for the keyword.  And I might be mistaken but my understanding is that Google disregards everything after the "#" so there shouldn't be a duplicate content issue.