1. If you are limiting yourself to a niche only, your blog is going to be SO boring. At the least, you have to interject #2. Everybody has written about every topic ever. Seriously. What do you bring to the table?
2. People know where to find me. With the advent of RSS, people can follow me in multiple places with minimal effort.
In short, I do a combination of #2 and #4. I probably did my first post on #3 and there was some interest in it.