In reply to Jonay:
> GoreTex Performance/Pro shell is the "thickest" decent waterproof membrane on the market at the moment [...]
This isn't right. The robustness of a waterproof laminate (or coated, come to that matter) fabric has little to do with the technology of the waterproof membrane (be it Gore-tex Performance Shell, Gore-tex ProShell, Event or whatever).
What determines how thick, heavy and robust a fabric is (or, conversely, how thin, light and fragile) is the face fabric used to make the fabric laminate.
The membrane can be bonded to a whole range of face fabrics. So, there are lightweight ProShell fabric laminates out there, and there are heavyweight ProShell fabric laminates. Just as there are lightweight Event fabrics and heavyweight Event fabrics.
Gore do tend to have a better range of better face fabrics in my experience.
Pertex Shield+ is a coated fabric, not a membrane, but is seems to have a pretty good breathability, as do many of the more recent PU coatings. Pertex call it a 'PU film laminate', so maybe it is a genuine laminate rather than a coating; maybe creating a film first allows them to control the thickness better than applying a PU coating.
http://pertex.worklove.co.uk/fabrics/shield-plus/
As with all things, the maxim 'light, durable, cheap: pick any two' probably applies. Lightweight fabrics have their benefits, but they also have their drawbacks, in that they are not as robust, and really shouldn't be expected to last as long as something with a more robust face fabric.