I can keep up with the speed with no problem -- super-fast typist here, and years of practice spent sitting around on IRC. But for me it's more of an emotional/mental thing, being "on" and live like that is more draining than something like LJ where you can take your own sweet time and go back to a post whenever you feel particularly alert and energetic. Chat, I have to be in the right mood to enjoy it, and if I try to do it when the mood's not there, it feels unpleasant, like the pressure of having to talk face-to-face when one isn't feeling particularly social...