Many people already use Twitter as their RSS replacement. In fact, I can’t help but think that Twitter’s rise in popularity had a direct impact on Google Reader’s decline. For my part, however, I hate using Twitter like this. RSS is nice because everything comes in flooding in, but stops, waiting on me to hit “Mark All As Read.” On the other hand, tweets stream by, endlessly, without regard to what I — as the user — am doing. If something goes by, it’s gone, unless I sync my timeline or read back until the point I left off.
While I empathize with Stephen’s point about the endless stream of information, Twitter’s become my de-facto RSS client. For better or worse, I barely remember to check my true RSS feed anymore -- and I have Reeder on the first Home screen of my iPhone precisely for that purpose. Reeder’s a great app and RSS a great tool, but I get most of my news from right within Tweetbot now.