I recently purchased the new bright ground glass and have now added a review of it to my Linhof Techno review:http://www.ludd.ltu.se/~torger/photography/linhof-techno-review.html#new-gg-review
(the web server is a bit tired so you may have to press reload a couple of times to get all images)
The short story is that compared to the standard glass+fresnel combination it's 1.6 to 2 stops brighter in the corners for wide to normal lenses, and loses about 1 stop for 100mm and up. Put in other words my SK35mm is now brigther than the 47mm was, and the 47 brighter than the 72, so even if 1.6-2 stop may sound moderate it does make a difference in practical use. The only disappointment I had is that it's a glare machine, as I like to compose without a focusing cloth. For those €700 I think they could have had some surface treatment.