Hi - obviously my contribution is a bit one sided since I only have an SL4 to tell you about, but I rode it for the first time this weekend and I was blown away with how quick it feels on the flat, downhill and climbing. I'm comparing it to a 2008 S-Works Tarmac (which was also written off by my insurers following a crash, which is why I didn't get to ride the SL4 before I got it), which was a light, quick and very responsive bike (but also super comfy as it had the zertz inserts in the frame and forks).
The SL4 felt stiffer and far more direct - it was super responsive (the slightest input gave an instant reaction whether it was accelerating, braking, or changing direction) but it also felt very stable - not at all flighty.
I did just over 30 miles, with a very big climb in the middle (up to 20% gradient). Given that it's got standard 53/39T chainrings and an 11-25T cassette, I was pleasantly surprised how it (and I) coped with the climbing.
On the 'mass produced' side of things, my view is that yes you'll see lots of Specialized bikes around, but you wont see too many S-Works bikes. Also, their s-works frames are (IMHO) as good as any more 'fashionable' frames (possibly even better) - have a look at this review attesting to the strength of the frameset:
http://www.redkiteprayer.com/tag/specia ... armac-sl4/" onclick="window.open(this.href);return false;