I've spent a total of 6 weeks - on 3 different occasions - on Koh Chang... always during Nov, Dec and Jan... before I went the first time I heard the horror stories of not taking malaria pills... I didn't bother and got bitten hardly at all (the mozzies are much more numerous between March - June I was told) and I was fine on my return... the second and third times I was on malaria pills anyway as I was also going up to the jungly North Western corner of Thailand... It's all about personal risk and what you feel happy with... It's true about the malaria pills and pregnancy thing though... maybe your friends can just 'practice' plenty whilst there and get down to the serious business of procreation on their return!!!...