Josh goes over the Nintendo DS Opera Browser for his DS Lite in a 7 minute review. If you're interested in how this looks on a real-life system, reading sites like Slashdot, Digg, and Gizmodo—Which looks and runs perfectly fine, says Josh, except for the Youtube videos, because Flash isn't supported. Loading is kind of slow, but functionality-wise, everything works fine.
Here's a followup review. Check out the video for all of his thoughts.
Nintendo DS Browser Review [Joshua Zimmerman - Thanks Josh!]