A few words to add to this debate:
I've got two Rab eVent jackets, one bought second-hand from a friend which is a few years old and one I bought new from Cotswold Outdoors in this year's January sale.
I've always used liquid soap at 30 degrees, a second rinse, then iron on the two-star setting through a thin tea-towel.
The older Rab jacket has always returned to nearly-new performance (cuffs seem to sometimes wet out, but nothing else). The newer jacket has only been worn twice in persistent rain and wetted out the first time I wore it from new. I gave it my usual treatment (as mentioned above) and its performance was again crap the second time I used it. So I'm not sure if some eVent fabrics are now being produced by an inferior company (somewhere in China, no doubt).
I wrote a letter to Cotswold on 15th June, explaining my plight and asking for their advice on refund or replacement. I've heard sweet Fanny Adams from them to date.