I have several garments made with eVent (plus many more in all manners of Gore, H2No, Precip, etc.). So far, I think that eVent is excellent, but there are some limitations. First it is surprisingly not 100 percent windproof. Maybe that's OK for most people, but I want something windproof when skiing downhill at 30 mph at 0 degree F.
I'm interested to know why you think it isn't windproof? I'm not discounting your experience, just curious. As most w/b membranes are completely windproof due to the fact that they have to be because of their waterproofness, I'm not sure how eVENT isn't completely windproof as well.
Air permeability, that which gives fleece and softshells a one-up on hardshells in terms of ventilation, is recorded through cfm measurements. The only air permeable w/b membrane that I know of is Schoeller's WB-400 which records 3 cfm (cubic ft per minute), helping it's breathability. This laminate, after it is applied, expands slightly resembling very fine foam. This 'foaming' action gives it it's air permeability. It is only used with 4-way stretch woven, or softshell, materials. All other membranes and laminates are completely windproof, or, in other words, record 0 cfm.