In reply to liza:
We went in October about 2 years ago. It was too hot, rather than too cold. As I said above, most crags are in the sun for most of the day, so it's difficult to find shade, except on Castelli.
The sea is always accessible (30 mins at most) and is lovely and warm in Oct. A lunchtime dip is very refreshing.
You'll find more info here:
http://www.ukclimbing.com/forums/t.php?t=56179
If it's at all windy watch out for cancelled ferries! We missed our flight and had to pay £300 to get home (to Heathrow instead of Manchester!) - but managed to claim it on cancellation insurance.