The Columbia disaster was the first disaster that I remember learning about on the web. I was up early browsing a news site when I spotted a little story about Mission Control losing contact with the shuttle during its descent. I then turned on the TV to the cable news channels to see if they were saying anything, and I saw the first video broadcast on CNN. I knew right away it had broken up.
Every disaster before that I learned about first on TV or the radio. 9/11 was the first time I tried to follow news reports on the web; I was lurking on FR even though I didn't have a user account yet. I remember I eventually gave up, because FR kept going down under the user load. I just started flipping the TV between ABC/NBC/CBS/CNN/Fox News...
Same here. In fact, I signed up here ~on~ 9/11. It was the events of that day that lured me out of lurkdom.