A very heavy going discussion is taking place over at the highrankings forum with regard semantics and what exactly is going on.
"When I first saw it, I was a bit puzzled. Wouldn't Google with such a complex algo already have placed heavy importance on it for rankings? Or, are they now just able to do it?"
(I suspect that at the first stages of Florida, they allowed it to work poorly - hence the weird results, and later tweaked the levels of semantical requirements to trigger the "use it or not use it" levels - and those adjustments continue today).
Was posted some time later with regard it's application
There are some links here to some superb resources, but be warned they are deep, and hard work, BUT that said, if you are serious about SEO, then you should read it Semantics, whats it all about? good luck, and pour yourself a cup of coffee before you start.