This evening, I used this programme which is supposed to tell you what Google are looking for. I spent ages condensing all my keywords and fine tuning my site description... only to come across a different programme later on in the evening which told me that I hadn't used enough keyword. So in they went again after I'd painstakingly taken them out an hour previous.
I'm calling it a night now as I'm
a) getting tired and
b) wondering if it's all worth it.
From what I gather, nobody really knows what makes Google spiders tick, so should we really spend our lives worrying about it?
My humble opinion would be: choose your keywords and descriptions wisely or at least do the best you can. After that, it'll be in the hands of the cyber gods.