I am an Evangelism Manager at Microsoft. Evangelism is the new style marketing (or maybe marketing is just plain dead). It's about the conversation. Two-way and open and honest.
I write because I want to remember (not per se to be remebered). There are so many interesting things I read every day, so many interesting trends, people, etc... In order not to forget myself I log something now and then to extend my public memory. I also write because I think I might save other people's time. The time it took me to research some stuff.
I have on and off times. I always express my personal opinion.