Also worth noting, LTspice lets you parameterize component values directly from within LTspice. You can set up conditions that drive a calculated value prior to simulation. There's also quite a good Yahoo group dedicated to all things LTspice.
There’s a further cool thing you can do with a spreadsheet that most SPICEs can’t. That’s to use the spreadsheet ‘solver’ functionality to adjust component values in the search for a better-fitting circuit – or even to find a set of component values for a circuit you can’t otherwise design.