Here's a post from John Davis, a respected watch maker on the Purists.com forum. I've included some extra links as well. Some of this is pretty technical, but it is very interesting information on hairsprings, and timing.
"As far as the movement is concerned, it is a wonderful piece of work that is exactly what it claims to be: a grand Seiko movement. The finishing is almost entirely machined, but machining of exquisite quality overall. The edges are generally not chamferred (anglaged), but are incredibly crisp and the sides are cut to a near mirror polish (as can be seen in some of SteveG's pics).
The technical selling points of the movement are these:
Seiko Magic Lever winding: possibly not a selling point in a $3k watch when it can be found in watches for $50, but what else could they do? Seiko invented the most elegantly simple automatic winding system on the planet and it just happens to be incredibly robust, long lasting, bi-directional and suitably efficient. Are they supposed to step down to something less functional for their flagship pieces? Come on.
The rest of the techie selling points (that I'm aware of, I have yet to actually dismantle/service the thing) are in the timekeeping arena:
In the movement detail above, you can see a little switch looking arm on top of the regulator. This is an mechanism whereby the distance between the curb pins can be precisely controlled and a fabulously useful device where isochronism adjustment is concerned.
Most watches with curb pins require the adjuster to squeeze the curb pins together or pry them apart to get the rate at different amplitudes to line up as desired, with the need to constantly restraighten the pins to perfectly parallel if the dial-up dial-down deviation is to be respected. Not an ideal solution by any means and when you eventually break off one (they are incredibly delicate), you will be one mad watchmaker, let me tell you.
Seiko's solution is elegant, simple and ingenious. Not as simple as the ETAchron solution mind you, but Seiko's approach doesn't involve curb pins striking the inside and outside of the terminal curve at different distances either, an annoying side effect of the ETAchron curb pin adjustment. Some older, very high grade movements employed similar curb pin adjustments, but Grand Seiko is the only modern watch that I know of that has one (other than the previously mentioned (and flawed) ETAchron system).
Another wonderful techie tidbit is the use of a Lossier curve for the innermost coil of the hairspring. This is an incredibly rare hairspring elaboration that is designed to act something like a Breguet (Lossier, Phillips) overcoil, but applied to the first part of the hairspring as it exits the collet (near the center, where it attaches to the balance staff).
Most pinned hairsprings (very few hairsprings are pinned these days) have a pretty sharp curve where the spring leaves the collet and then the spring developes immediately in the same manner as the rest of the coils of the body of the hairspring. This initial, drastic bend of the hairspring has enormous impact on the way the rest of the hairspring developes during expansion and contraction and generally introduces a pretty chaotic factor into the whole equation.
Modern hairspring collets due away with this first bend altogether by crimping or laser welding the spring to the collet without bending it at all, but even this is not an ideal solution. Asking the spring to go from fixed to perfectly expanding and contracting coils with zero transition is a pretty tall order if a smooth, even response is desired.
A Lossier inner curve developes in a precisely controlled evolution for the first 270 degrees or so before entering the normal body of the hairspring and, if perfectly formed, can contribute greatly to the isochronism of the oscillator. If anybody is really interested (and not yet been put completely to sleep), I'll see if I can dig up a picture of this mysterious sounding inner coil from the Seiko book.
Most manufacturers abandoned Lossier inner curves long ago (outside of chronometer competitions at least) as being too difficult to properly implement with consistently good results (the same way overcoils have all but been abandoned nowadays in mass production). Unless the Lossier inner coil is nearly perfectly formed, the benefits will be basically nil, and forming them perfectly on such a small scale (the first coil of a hairspring is pretty tiny) is not at all easy to do.
Seiko on the other hand worked extensively with Lossier inner coils (couple with overcoils) in their chronometer competition pieces (their fabled Swiss killers) and apparently had good luck. Enough so that they still use Lossier inner coils in their Grand Seiko and similar high-end movements, even without overcoils.
In all honesty though, I think the best reasons to buy a Grand Seiko are completely irrational. The anti-Rolex effect of having basically no-one take a second look at your watch and, even when they do so, generally writing it off immediately when they see the name on the dial is an wonderful, personal pleasure. Of course most would never guess that it would cost more than a hundred bucks or so, so you just smile at it and to yourself when they dismiss it at a glance. I try not to even talk it up too much in converation unless someone is really interested. It doesn't need me defending it, that's for sure.
Every once in a while someone will "get it" however and it's a great joy to share their appreciation for it when that happens. The steel is of a different type and quality from most other watches, and shows a slightly different color in some lighting. This is an immediate giveaway to someone attuned to such things and they'll see it and immediately think "nice watch" even if they second guess themselves when they see the Seiko name. Then when they take a closer look at the dial and hands (truly, these do not give an inch to anything else out there at any price range) and the attention to detail and quality of the case and bracelet, their initial impression returns even stronger. Then you can both smile together.
Japanese Watch Enthusiasts: http://www.gmtplusnine.com