I held the top spot for search terms relating to my service and site for more than a decade, until I shut it down. I never spent one second of my life worrying about SEO. I focused on usability, generating word of mouth (far more valuable - how do you think people found out about Facebook and Twitter?), and content.
The nature of a search engine is to derive the value of your content from the content. Therefore, focusing on your content is a far greater return in value than focusing on trying to draw the attention of a search engine to tags, meta data, or URL paths. Not saying that those things don't contribute, but I'm not certain that the ROI is worthwhile.
Think of it like a resume. If you have the talent and background to put on a resume, you'll get consideration. You don't need to spend hours upon hours refining it to add just the right trendy keywords or ordering things in the most appealing way to automated resume readers. On the other hand, if you have little to offer and you are concerned that you'll be weeded out quickly as a result, you can substitute your background and experience (content) with keywords and other tricks to try and get beyond the initial weeding out. Kind of a tactic of desperation and lack of confidence.
I do have a strong bias against the whole SEO thing. I won't pretend that I don't. I'm put off when I hear people focusing on it rather than content and it makes me think of greasy, scummy, snake-oil salesmen. Guys on late night infomercials trying to convince you that you can skip everything and get right to becoming rich and famous by thumbing through their special book and employing their special techniques for flipping property with only two hours of work per week.
This is probably a very unpopular opinion to share around a group like this, but what can I say?