Could I jump into the conversation +Darren Rowse
and +Daylan Pearce
please? The fact that most pitches reached you were rubbish says something, isn't it? It means the real good SEOs, the ones that really get it won't contact you unless the content and relevancy are absolutely spot on.
SEO is no longer SEO now, I'd say SEO is 90% content marketing, content in the form of blog, inforgrahic, video, tweets, G+ posts, seminar, etc. To evaluate a link and see whether it's good or not, you just need to simply look at the traffic referral rate (number of clicks on the link divided by the page visit). Because audiences tend to click more on a link when it really means something.
And a good link building (I hate to use this phrase, because it bears such a bad reputation) campaign will not only help with keywords rankings and organic traffic, it also should generate many referrals as well.
I had one post before which generated over 1000 referrals in the first month the post went live. That's 1000+ targeted audiences - better than organic visit! I didn't even need to care whether Google improved our ranking or not. And I am sure the website was happy with the content too due to the fact it had pulled in tons of visitors, and if it wasn't for the content, those organic visits could have gone to other sites.
The principle is simple - mutual benefit. The hosting website gets quality content, organic traffic, new audience, stickiness, etc, the guest blogger gets referral, exposure, recognition. Let just forget about Google, or any other search engines, let +Matt Cutts
and Co. scratch their head trying to surface quality content(we don't have to worry anything at all, because if they can't deliver good search result, then they are doomed), and let us - SEOs, bloggers, publishers, marketers - focus on delivering quality content and make the audience happy