It's a marketing "truth inflation". It's actually 200Hz refresh for all three subpixels (red, green, blue) independently, but that doesn't mean it's simply added up to 600... Still, 200Hz overscan is quite enough for any kind of fast motion. Some of the better plasma TVs will actually calculate and add frames into animation to achieve higher framerates (interpolation), most of the time this works fine, but sometimes the predictive logic can get things wrong and then it just looks weird and out of place. Luckily it can be turned off when needed.
Plasma's strengths are vastly superior black levels and contrast ratio, great color reproduction, quick refresh rates and good framerates; it's negatives are high power requirements and heat output, and some concerns about phosphors' longevity - though this is yet to be concretely quantified, especially for the newest generations of PDPs (plasma display panels).
I myself would go for a Panasonic plasma, but you should be aware that it never produces a static image. When you ask it to show one, it will internally divide the picture into domains (groups of pixels), then rotate the color/contrast inside each domain within 2-3%. The net effect is that of having thousands of little circular motions over the image, making it appear as though the image is "boiling". Panasonic calls this "pixel orbiter", and it's a measure to prevent image burn-in. This is a phenomenon that occurs in any display type (just take a look at some monitors - LCD, CRT, whatever - that have served for years in video surveillance, you'll see they have grids burned into their image), with the plasma being the most susceptible. By varying what each pixel shows to a small degree, the effect is minimized, since you're not actually showing the exact same image (thus keeping the pixel in the same state) for prolonged periods of time.
If you can live with the small caveats of a plasma TV, you can enjoy the best image quality available today. However, if it's primary purpose would be desktop use and internet browsing (where the orbiter effect is actually perceivable), rather than entertainment (games, movies), then perhaps a high quality LCD is a better solution.
