SEO as a business seems to me fairly nebulous and a bit like selling snakeoil. Techies are normally more worried about how the (web-based) system works, but the clients are more interested in the marketing. Which makes sense really, why would they want to spend money on us building systems for them if nobody visits. So, the practice of analysing logs and creating copy which hits the right keywords, etc. has grown into a small, but profitable business. All those people who used to be making profits knocking up websites are now making it by tuning them for Google et al. It may be a lesser skill than designing a complicated system.
Google AdWords is an excellent tool because it gives you loads of stats about who has clicked on which adword and how much it will cost for you to be higher up the list. This got me to thinking, the user may have clicked on the adword but did they want what your site offers, did they stay, and did they purchase anything.
We've been using clickstream on our sites and what i'd really like is a special Google AdWords extension that will make particular notice of someone arriving on my site. I guess that measures would be: big score for a direct purchase; medium score for looking around the site for a bit; and a low score for not staying (because the site didn't meet the user's expectations of the keyword, or because the site or product didn't meet their expectations of quality).
Unless you are selling consumer goods online it can be a difficult thing to prove whether a visit causes a purchase. People often have many points of contact with a product before they buy. For example, when I used to run a system for a major cruise company I analysed the conversion rate from people ordering brochures to ordering a cruise. The direct rate was worryingly low, but the results of the analysis were that people often order brochures and then go on a cruise in a completely different region, or they book a cruise two years after looking at the brochures, or the sum total of newspaper ads, brochures, tv travel shows eventually adds up to convince them that they want to book, and all those points of contact are not registered anywhere in your data.
My conclusion: a great system delivers what a client needs, in business the base need is generally profit. Integrate marketing functions into your system.