I think it's an individual decision depending on the type of blog you have and what you want to say. If you use your real name and discuss personal issues, you need to think about any possible repercussions etc. As you stated already, you are questioning what you can write about! because your friends know you.
I use a nickname which is catchy, but there are people who know who I am, and I don't mind that. I say what I mean and hold dear to what I say.
I've struggled with this a lot. In the blogs that I admire most (e.g., Sam Harris'), the author's use their real names, have their photo on the page, etc. Of course, these are often blogs by 'public figures' who have chosen to be 'in the public eye'. I chose to go this route. But it was a difficult decision, because I have another website associated with my work (I'm a professor and neuroscience researcher) - and I didn't really want people who 'Google' me to show up at my blog (which includes both science-related but also more personal posts). The safe choice would be to use a pseudonym, but I chose to 'live out loud'. :)