I don't think that there are any hard and fast rules, they CAN charge if you are over the weight limit but don't always do so. From the thread that Sailor mentioned I have to admit to being quite nervous when we checked in for a Brittania flight to Corfu, (from Gatwick) although Debs has nothing to wear it seems to weigh quite a lot (oh OK I do need a lot of shirts too!). We were about 7kilos over the limit and not a word was said. On the way back having discarded part used toiletries we were still overweight by 2 or 3 Kilos but again nothing said.
So the same airline and no action, the flight was not full and that may have had a bearing on it. I seem to recall that the limits used to be 30K and I wondered if the airlines reduced it to 20K to try and stop us all exceeding the 30K limit?
I suppose in time we will all be weighed and our baggage allowance dependant on our weight! Afterall there must be a maximum payload that they can cope with.... It would mean certain diet for me so that I could take enough shirts!
I am flying with Kosmar/Islandsflug in September from Bristol, it is only a week this time so hopefully we will keep within baggage limits, but I will be interested in your experience.
Have a great holiday.