Three cheers for Nintendo - turns out that, for once, Nintendo is doing a a lot of cool stuff based entirely on open standards. Like Wi-Fi. And to top that off, it appears that Nintendo's own Wi-Fi adapter for PC is actually completely Linux-compatible. And the craziest part appears to be that you can use stock unmodified Nintendo hardware to run homebrew games over Wi-Fi.
Yep - rt2570 driver recognises Nintendo Wi-Fi USB Connector. Set it up, fired up Ethereal (should upgrade to Wireshark =), told Nintendo DS to look for a network, and stood in awe as broadcast packets appeared in Ethereal.
The thing is, it ended at seeing the broadcast in Ethereal. Of course, DS couldn't find an AP. Hardware is apparently the easy part. Now, to actually use DS networking, I'd need to make the dongle to actually respond to AP broadcast, set up the link, and route my packets. In other words, I need the SoftAP part for Linux. Easier said than done, it appears that host-based AP stuff is supported for certain hardware, but I couldn't find that for rt2570...
(There bloody well has to be a way to do this. DS Wireless Multiboot has to be harder to hack together than a minimal AP thingy.)
Also, Tetris DS seems to rule. Tetris is always Tetris, of course, and the new game modes are very interesting. To honour the return of classic to the new machine, I tried playing the game for the first time while wearing the original GameBoy headphones... =)