I used to do MAC whitelisting, but it's annoying for the fact that I fix computers, and wouuld have to whitelist every new computer to my network... so no thanks. And the DSi can use WPA for eShop and web browser, but not in-game. The games only support WEP. I'm just too lazy to go into my DD-WRT setup and create a WEP Virtual LAN for my DSi at the moment.Link_sys. Because the default Linksys was already in use in my neighborhood and I wanted to avoid confusion.
DSi supports WAP, no? I use WEP as well so I can use my DS Phat and my kid's DS Lite on line. I use MAC filtering as well, but rather than blocking moochers (black-listing,) I only allow devices that I manually key in the MAC address in to my router setting to join my network (white-listing.) It's a bit more work, but it's the safest way to use WEP that I've found.