Some personal impressions after finally holding this infamous color chart in my hands. Even though descriptions of colors are like... well, never mind, can't think of a good metaphor. If you didn't get a copy yet, and still haven't made your color choice, see your dealer!
Ardent Red: Looks darker than I expected. I had gotten the impression that it was a fairly light red from some of the pictures. It's a solid, deep red.
Saffron Yellow: Looks darker than ACP's pictures did on my monitor. I might have prefered it a touch lighter. But it's a nice, clean yellow. I can't really see the orangy tone that some people mentioned. From memory, it seems quite comparable to the yellow on a Z06 or ITR.
Magnetic Blue: I'll have to hold it against my car when the sun comes up again, but I believe it's darker than the WRX blue. But a similar character, very nice color.
Aubergine Purple: I don't like purple cars. I think it's ugly.
Aztec Bronze: I thought I might like it after being quite impressed by a couple of orangy/bronze cars. Not impressed by the color sample, though. It almost looks gold. Coughpimpycough.
Racing Green: Not my favorite, but I think the people who chose it looking for something more low key will be very happy. Very tasteful and classy color.
Starlight Black: I normally like black cars if the owner keeps them clean. For reasons that I can't pin down, I don't expect this car to look good in black.
Bordeaux Red: Similar to RG. Not necessarily my thing, but a very good color.
Nightfall Blue: It's dark. I mean REALLY dark. Almost black. I dunno, not my cup of tea.
Storm Titanium: As others mentioned, it's very sparkly, with a lot of texture. Very hard to tell from a small sample how it will look on a car.
Arctic Silver: Well, it's silver. What more can you say.
Chrome Orange: It's slightly metallic, but still looks a bit "flat" to me. The dealer was all excited about the color. Told me how everybody loved the CO Esprit they got, and that he chose it for his own Elise. I'll probably like it, but I wouldn't want it for my own car. It seems like something I could get tired of after a while.
Graphite Grey: Darker than ST, with less texture. Another classy color if you want to keep a low profile.
Krypton Green: I admire the courage of people who order it!
A small part of me thinks that it might have been an interesting choice.
Sorry about the long post, I hope it helped somebody.