Match, that knot has to be one of my favourites. It's so simple and yet so clever, and very effective.
In Skye earlier this year our tent was suffering in the wind. The guylines used plastic toggles for tension, but they soon became loose in the buffeting gusts. So I ignored the toggles, used the adjustable grip hitch, and the guylines were fixed.
Gaz, most of my (limited) knot knowledge is from the Ray Mears book as well - very handy set of knots. Always practice with cord while reading them, though, as they'll make much more sense. I'm always a fiddler, so recently I've taken to fiddling with a piece of cord and practising knots. It's a great way of learning - eventually your fingers know what they're doing without you having to think.