[Rankenstein]

I've always thought you can reasonably go for two, three is doable, four is too many but it depends what you consider as different keyphrases. So if I was selling blue, red and green widgets online in the UK I'd try something like:

Widgets for sale - Buy blue, red and green widgets online in the UK

and that should fill up the title bar on Google, and allow a good mix of phrases - more than four, but then they're not massively different in the mix.

That's what I think anyway.