At this point, coming to the end of Wrath, and with the release of Cata just over a month away, starting a WoW blog could appear an odd endeavor. The game is definitely in pre-expansion doldrums fight now. Most of those that are going to down the Lich King have done so and are looking for new accomplishments in game, or even turning to other games. Sever populations are down noticeably, and many guilds, if not most, are in pretty rough shape, having a hard time pulling together to raid.
And yet, that makes this a good time to start a related endeavor like a blog. With less to engage in game, there is time to start producing some content, developing a site look and feel, and take care of all the technical issues that come with running a blog and a web site. With that done now, there should be some momentum to continue the blog going into Cata.