For a good few weeks now I've been driving around, heater on, completely forgetting about using the A/C. I'm sure I read somewhere (the instruction book? duh) that the A/C should be used on a regular basis to keep it all in good working order. Any A/C experts out there who can tell me like it is and what I should or shouldn't do?

It is good to use it in the winter anyway as it helps to dehumidify (and therefore demist) the car.

Hot air is channelled through the compressor which causes most of the moisture to condense and then you get warm dry air blown in to the car.

Its good to turn it on from time to time, as it will prevent leaks from occurring due to the seals drying out, and it keeps lubricant flowing to keep the system running smoothly. Once a week is good I'd say - there isn't any "correct" frequency really.

But I personally wouldn't keep it on all the time in winter, as it just unnecessarily yields lower MPG. As long as you have the re-circulation button OFF, the windows demist and cabin dehumidifies absolutely fine without needing the A/C.

Use it at least fortnightly otherwise the seals dry out, leak and you lose all your gas.

I should have probably said I didn't mean all the time, I only turn mine on if the mist is being particularly stubborn, but I do notice that if I have used the A/C the day before the car is never as bad inside.

On my Focus (and Fiesta before it), if you pressed Max Demist, it turned A/C on anyway,

Just to add to what's already been said, the coolant in the air con system contains lubricant. If the aircon isn't on, the seals don't get lubricated, they dry out, then they leak, and you have a costly repair bill. Watch this forum around May or June (assuming we aren't in the middle of the next ice age by then) - I guarantee it will be full of people asking why their aircon doesn't work any more. And that's why.