Hello danimal:
There are several related threads on the new LS2 rods since October of 2004.
The action on the series is what I would term medium fast, compared to the industry average. They are indeed among the lightest, if not the lightest, rods around... Since I often like to try to hold a fly on a good looking seam or pocket, frequently by holding the rod by the butt as high up as I can, lightness goes a long way in reducing deltoid fatigue over the course of a day. A light rod can also be just as powerful and precise as a heavier rod, perhaps even more so, and a lot of work went into the taper of the rod to balance windage vs. stiffness (you can have a stiff rod with very thin walls, but end up with a really wide diameter). A light rod also has a lower swing weight, so the theoretical max tip speed is increased, and it balances lower into the grip (as opposed to on the blank itself higher up) through the swing, which is simply more comfortable while fishing.
Casting wise, we wanted a rod that didn't have a wimpy tip, and that gave some real "pop" to the cast and wouldn't fold over with a heavy sink tip. A rod which casts long belly lines well will also cast short bellies well (but not vice versa), so the rods were all designed to excel with long belly lines. The action is progressive, meaning the rod just doesn't fold over in one place as more load is place on it. We did a lot of high speed digital video analysis tuning the actions.
These rods essentially represent my idea of what a modern spey rod should feel like in action and performance, and what modern technology and materials can provide in terms of a great power to weight ratio. Jim Bartschi, the rod designer from Scott, was able to take four years worth of input from their pro staff and morph it into reality. Plus, they retail for less than $600, something else I felt strongly about!
There is always a payoff between high performance and durability, which was also one of the primary design considerations. If you want a bombproof rod, it will be very, very heavy. Even really heavily built rods break, irrespective of manufacturer (like one of the Bruce and Walker 18 footers during the Musto this year). However, the A2 rod series, themselves among the lightest around before the LS2's, are known for their durability. I torture tested prototypes for the LS2's in Russia for the past two years, and think that there will not likely to be any more breakage problems with the production layup of the LS2's, despite their lightness, than any other rods I own or have fished.
I hope this helps... Just like purchasing any other rod, the only way to really tell if you are going to like a rod is to cast it! (I know Scott is currently quite backlogged for the LS2's due to much higher and unanticipated demand from Scandinavia and Japan. Hopefully they will get caught up soon!)