Good luck today Nigel,
To anyone that
does need to 'break the rules' after the event; e.g. they have accidentally captured a wonderful cameo within a larger image, but it needs a severe crop to obtain a good composition (which will make the noise visible), I would recommend
Neat Image. It samples a blank area of the image, determines what the noise problem is on that shot and subtracts it across the image (I guess this qualifies as one of Colin's "fancy algorithms"
).
It works stand-alone, or as a plug in with most photo editing software (not 64 bit CS5 last time I looked though). It is also good for RAW shooting compact users, as I was when I got it.
Now I have a DSLR, it is true I don't use it often, usually only for the example given above, or ultra high iso shooting (e.g. 3200 and above), because, as Colin and Robin say, as long as a shot is well framed and well exposed when captured, noise
won't be a problem.
Cheers,