I've looked at all the iPod docks for years and thought, man, that sure would be nice. About a year ago, Creative had all their new about releasing the Z-500, and I got pretty excited. And, then, as you know, they didn't release it, and didn't release it, and didn't release it. Then, I found pictures of the Z-600. The Z-500 wasn't good enough anymore, so even when it was finally available in the US, I didn't get one.
So...same story on the Z-600... It appeared they were never actually going to release it in the US. I saw a few go across on ebay but they always went for really high prices, and I just wasn't willing to spend $700-800 bucks on a simple 2.1 speaker system. I gave up.
I finally went back to Creative's website about a month ago. They had one in stock!! Score!! A few days and $300 bucks later, I was hauling a heavy freaking box up the three flights of stairs to my apartment. Whew. I didn't think the sucker was gonna be that big.
I opened the box, and....
Yup...
It was as beautiful as the pictures. Sleek and shiny black. And the sub is a fricking 10"

What the hell? for these little puny speakers? So...a few minutes later I finished plugging everything in and dropped my nearly three year old ZVM into the dock. The pretty blue light comes on, and its music to my ears. Literally as well as metaphorically.
I'm actually not that big of a fan of the X-fi crystallizer and the CMSS 3d sound features, but the speakers and sub produce crystal clear sound, at both low and high volumes. And unfortunately, I had my neighbor from two floors down and across the way actually come up and knock on my door asking me to turn it down...oops. So it does get pretty loud.
Loudness aside, the speaker system produces really really nice sound. The CMSS and X-fi can mess with music that is already well balanced and mixed. I tend to keep my music files at 192 Kb or better, so the X-fi is not needed that much anyways. However, it does actually help on some of the lower quality files that I have thrown at it. With tracks that are mixed to incorporate 3d stereo already, the CMSS can really make the tracks sound hollow. Typically, I leave the CMSS off, and the X-fi on a very low setting.
So....the golden question....is it worth 300 bucks? For me it was. If you already have a decent receiver and speaker setup, then maybe not. You'd probably be better off going for the Xdock, or some other method of getting remote control ability over the ZVM.
I've got my DVD player and junk routed through my TV, and the audio out of my TV going to the single rear input on the Z-600, so my setup is somewhat rigged. However, it does work, and the z-600 speakers are much nicer than my TV ones. The best part of the setup is the remote control ability over the ZVM. It's kind of annoying watching a movie on the TV from the ZVM and having to get up and press pause every time the wife wants to say something.

The speaker quality is definitely nice, but there are some other options for $300 that could probably equal or better them. So...if you need a speaker system, and happen to have a ZVM that you want to dock, the z-600 is amazing. If all you want is a speaker system, its still worth a listen, but I wouldn't be too surprised if you buy something else.