I have all the washes (I am using the GW paints) though I tend to use them somewhat early on, after the base colour goes down and then try to highlight up from there. Blending is the biggest issue that I have, so I may try putting some washes on at the end, but I've found that they make everything darker...
I'm also not sure of any washes over flesh as the Ogryn Flesh wash is extremely red and makes everyone look sunburnt.