1. There is no review panel or editor preventing you from making an ass of yourself, including publishing something just plain wrong.
2. You’re paranoid everyone is trying to steel your best ideas and want to be first to publish.
3. You’ll publish fewer “journal” papers because it’s already on the blog, and that’s good enough — it’s only read a few (thousand) times a month anyways.
4. You’ll get frustrated by the ~100x increase in readership compared to your journal papers, but still no credit from your institution.
5. You’ll start obsessing over the number of hits, links, and time on pages based on location and speculate who it may be.
6. You’ll have to argue your research with suddenly informed relatives over the holidays.
7. You’ll start telling everyone to “read my blog,” and tell everyone else they need to start their own research blog.