I suspect there are 2 kinds of people who'd buy a running watch of the rs-800sd caliber: the first are highly competitive or enthusiastic runners, and the second are gadget freaks who tolerate running and want to measure results.
I'm the latter, and I've been having a great time running with this watch. Just seeing the graphs of my performance change over time is motivation enough. Some quick thoughts:
1. Before buying, visit the Polar website and use their "compare" feature to see if you need the 800, 600, or 200 series. With the 800 you're paying a premium for a handful of features you might never notice.
2. The "sd" in the name is misleading. The watch included is the same as with the rs800, but it also includes a stride detection unit that attaches to your shoe. With the shoe sensor, you can glance at the watch and see your pace, stride length, etc. It's totally impressive once you calibrate it. You *can* buy it later if you like.
3. Still, I'm finding that despite calibrating the stide sensor, I'm getting 3-4% inaccuracy in my measured runs on a treadmill. If I run exactly a mile, it tells me I ran 0.96 to 1.04 miles. Not bad, but on a perfectly flat surface at a constant pace I'd expect a little better.
4. I think the stride sensor is a worthy addition, but if you're a fan of Adidas shoes, they make an "Adistar" model with a built in sensor. It's designed for this watch.
5. The heartrate sensor is perfectly accurate in all my tests and the included strap is comfortable and doesn't slip.
6. I haven't figured out if it's possible to change the volume of the heart-rate warning on the watch, for zone-controlled runs. If I exceed my goal zone during a Central Park jog, it beeps so loudly and continuously that it's embarassing to me and annoying to others. Which....makes my heart pound. I've figured out how to turn the beep off, but that's no good. I'd like it softer. Anyway, for those of you who run with iPods, the beep will penetrate your music.
7. The watch communicates with your computer via IR. MOST desktops and SOME laptops do not have infra-red ports. You can use any USB IrDA (search Amazon for it) dongle and you don't have to buy Polar's own branded one. However, if you use Windows XP 64-bit edition, good luck finding drivers that work. If you don't know if you use xp-64, you don't, so don't worry about it.
8. The Polar Pro Trainer software that comes with it is intuitive.