For me personally, search engine traffic whilst a useful tool is not the most important thing.

I think if people go too far over the top with SEO it does more bad than good! I personally deliberatley write my posts in the way that I speak or think - to try and include words simply for search engines is not blogging, really. After all, its my blog not Google's!

As for categories and tags... I aim to stick each post I write into only 1 category, the main topic of the post (eg. "Radio" is one I frequently use, my area of expertese!) and then use the tags to look further into the category and tag specific things. I don't think of them as meta tags (something I never really understood anyway) but a list of things mentioned in the blog... usually 1 per paragraph as each paragraph represents one line of thought.