I normally power up whenever too -generally out of frustration ;D
Replying to comments can take a massive amount of time, especially if the comments received are meaty. I often tend to get meaty comments where people have taken the time to think and write, so I feel I should take the time to think and write back. This might change over time, but I always hope that people would spend time reading the comments of others too and starting alternate conversations and relationships, rather than relying on the author. This way, the content itself becomes more important than who wrote it.
I usually comment first, then read the whole string. Sometimes I even stick my face into another commentator's remarks.
It's often where you see the very best of people-when they are commenting without orchestrating every word.
I like this happening a lot. It makes the discussion far richer.