I contacted Aegean ref the 15 kg allowance 'free' in 2010 to ask if we can pre book an extra 5kgs each. Thier response was
"The luggage allowance for Onur Air flights in Summer 2010 is 15kgs per person. Unfortunately you are unable to upgrade to take 20kgs, if you are over your 15kgs allowance you will be charged £8.00 per kilo that you are over".
Looks like I need to buy some lightweight luggage!