Ask HN: Niche blog+jobs in your area of expertise

I have been thinking hard of building something as a viable online business and after going through so many cool ideas, I am seriously considering settling down on an idea of starting a very specialized niche blog which hopefully can turn into a SAAS business later on. The idea is to engage and get a good chunk of users (critical mass) to register and follow this blog all for free. Once critical mass is reached, I will open it up to recruiters etc. to start posting jobs in that niche. This is a very specific area that I already work in and the first 100 users will actually be my co-workers. What do you guys say ?