We enjoyed a couple of remarkable nights when by rights we should have been bitten to death (shady, windless pitches, in the trees, beside rivers, in July) but weren’t. The common factor to my mind was the use of midge coils. I didn’t believe they would do any good but it seems they did.
We had a campfire each night as well, so perhaps it was the combination of the two.
Smidge repellant seems to work well, and not as greasy as Avon Skin-so-soft.
edit: Oh, and the comment ^ about black clothes, very true, I usually wear black merino and its repulsive how many of them you see crawling all over it.