I have tried the Avon Skin so Soft and it definately works. If you google it, apparently it is a bit of an urban legend and there is no science behind it at all.
Put it this way - usually if 2 of us go away, I will get bitten alive and my partner will get none. Since I discovered the Skin So Soft, I have had about 3 bites per holiday as opposed to about 30 before.
It's only the stuff in the greeny coloured spray that works, none of the perfumed stuff - far cheaper than mossie repellant I was buying from Boots before :-)