This is very nice news. I've been using Opera for years, and I've been hoping to see it on the DS since it was announced. If you'd like to get an idea of how Opera DS will render pages, download the desktop version and browse your favorite interwebs in "small-screen mode." View>Small screen (Shift+F11).
Nintendo's new website incompatibility was weird. The last time they updated the site, Opera worked as poorly as any other browser from the get-go. I promptly sent them a snide email pointing this out. :¬]