When thinking about what I'm going to do to optimise my website to ensure it performs well on the search engines, it's easy to forget about the fact that I'm building the website to attract users, and business. Which is it more more important to optimise for; search engines or users?
The honest answer is that you should optimise your website for both search engines and for users. If you don't consider the search engines when creating your website, you run the risk of not performing well on the search engines which could mean a significant loss of traffic to your site. On the other hand, if you optimise only for the search engines and don't really consider your users, you may end up with a website that your users don't like or appreciate meaning a loss of conversions. i.e. Lost business and revenue.
The search engine optimisation process should involve taking a broader view of your website. You need it to perform well on the search engines, but you also need it to generate sales and income, if its a commercial website. So, ensure your website is as search engine friendly as possible, and also ensure its full of well written quality content for your users. Failure in either area will result in lost opportunities.