creep, stretching (need to adjust the rigging on the water), fatigue (especially where our stays bend around a rotating mast), difficulty with terminals/eyes, lack of easy adjustment and longevity vs. cost has been the reasons quoted.
I like the idea of synthetic rigging, so I am hoping for positive reports from you

How did you rig the shrouds and ensure adjustability?

Interesting negatives and the usual ones. Creep shouldn't be a problem as yes you will get minimal creep but your adjusters should take care of that. My biggest problem with creep and stretch so far is that the line is so under stressed it takes a few sails to really tighten all the weaves up ( the 3mm doesn't seem to have the same problem as 3.5mm I've been using ). I'm thinking of some way to prestretch the rope in a hydraulic pipe bender.
Up until now I have used a standard adjuster on the rear stays and multi loop forestay to bridle line to take up any slack when rigging, if you fit a steel wire thimble in the eyes they work exactly as a steel wire loop ( I'll take a couple of piccies over the weekend ). However I'm tempted to do away with the rear adjusters as the rope is so easily respliced up a few mm that once you have your boat dialled in, do you really readjust on the water.

I like the D12 around my carbon mast as its soft and doesn't wear away the even softer carbon, from my experiance of trying to cut it with a knife it is very wear resistant and I would almost say that it is pretty unlikely to get cut on anything that another boat could through at it in a collision. Equally the old nutmeg of what about in the boatpark, wire is probably even easier to cut with a good set of wire snips, D12 is really tough to cut unless you have the right equipment ( kevlar cutting scissors )

Cost is a non issue, each stay cost me about £ 16.00 and it is as adjustable as I like, a wire stay has to be made by the local chandler and is a one time operation, once the ferrules have been crimped you cannot alter the length.

Any more for comments, I haven't yet had any safety issues raised ?. My gut feeling about this is that the reason why we don't use it more for stays is that we have always used steel wire so therefore it is still the best traditional way of doing it.