1Up has some nice hands-on impressions with the Nintendo WiFi Connection using the DS, and they confirms pretty much all the details previously reported here including the lack of support for WPA encrypted wireless networks.

Interestingly, the article also discovers that the Nintendo WiFi connection also supports Macs without need for any workarounds:

"f your home or school or office is already wireless, there's a good chance you can go online with your existing network. In my case, I was able to use the Apple Airport Extreme I've owned for the past two and a half years to get online, and it was nearly as simple as using Nintendo's software -- despite the fact that it's not officially supported. The DS's WFC Connection functionality automatically seeks and locates all available access points, and from there it's a simple matter of entering the HEX equivalent of the network password. Simple, fast, painless."

Unfortunately they were not able to stress test the online connections due to a lack of folks online, but the scene could change come November 14th once the first WiFi-ready DS games (including Mario Kart) launch.  Expect to see more reports pop up before then.