The G600 has some nice features. Its wireless capabilities give it flexibility, as does its support for Gigabit networks. The UPnP serving support was a nice addition to the box, as was the ability to add external USB disks.
But I found a number of drawbacks as well. From the start, the fan noise was an aggravation, and the inability to configure the device from my iBook was an annoyance as well. The performance boost of Gigabit mode was minimal, and although it was nice to have wireless capabilities, the feature set of the device in access point mode was limited enough that you'd probably be better off using a cheap full-featured device for your wireless needs.
Comparing the G600 to similar "BYOD" products in its class, I'd rate it lower than the Buffalo Kuro Box, Maxtor Shared Storage Drive or Synology DS101. The G600 has fewer NAS features, is noisier, and has lower filesystem performance. But on the plus side, the G600 has media serving capabilities that the others lack.
As far as cost/performance, you can pick up a 200GB Maxtor Shared storage on-line for around $240 including shipping, while the G600 will run you about $150 without a drive. Add a new 200GB 7200RPM IDE drive for $70 and you're just about even. Of course the Maxtor has no wireless, but a cheap access point can be had for $20-$30.
Put another way, the G600 isn't the most flexible or speediest NAS available, but its unique combination of wired and wireless connectivity, UPnP media serving and BYOD format just might fit your requirements.