dyslexics of the world untie!!
It's rife in the real world too, as nobody seems to know or care. I even saw a beer fridge in a shop in February that sported a sign saying "cold beer's" - just what was the apostrophe for? It wasn't hand written, it was embossed in white plastic on a drinks fridge. No wonder we can't spell as a society.
I realize I'm late to this discussion, but as an American in Calgary, I'll just point out that it doesn't bother me to encounter British versions of words (storey, centre, and so forth). It didn't bother me when I read books or papers by British authors before I moved to Canada, either, so if you are more comfortable with that, I don't think it's something that is a deal-breaker for American audiences.
Here's my personal take on your concern: Use the language that you're comfortable with. Simply use your English if it sounds natural. Your audience will understand whether the one reading your post is an American. Some readers can feel if a blogger is trying to pretend that he's someone he's not. I have also read a number of blogs written by British writers and I have enjoyed reading it. It's a good feeling to read a blog with a slight different tone and spelling. The search engines, on the other hand, got no problem with it. As I see it, you'll be good as long as the post is written in high quality. On the other hand, it might be better if you'll consider having two English blogs that targets two different audiences. This technique is pretty a waste of time and it's inevitable to have duplicate posts. However, the final decision is all up to you.
do you proofread your content yourself?? does it mean that you know uk/us english rules well? i personally think that there is not much difference and people would not even notice the type of english you use. it definitely needs to be written by a native-speaker and proofread. that's it.