I spend far too much time reading other writers' blogs. I don't know what I'm looking for, but I do know what I've found.
I've found that some successful writers--successful meaning regularly published--aren't particularly good writers. Their blogs are filled with typos, grammatical errors, spelling errors, and misused words. One writer at a group blog I follow is so bad that I actually pity her copyeditors. She must be one hell of a storyteller to compensate for her poor writing skills.
Am I being too harsh? Is she just bashing out her blog posts first draft with nary a moment taken to proofread what she's typed but actually turns in clean copy for her paying gigs?
But I think writers are known by the company they keep, and the company writers keep are words. If your blog posts are consistently sloppy, you might be better off not posting at all rather than demonstrating to the world that you lack basic writing skills.
Words are the company you keep. Use them well.