When we do stupid things on our own, they usually don't come back to haunt us. Nobody has to know that you accidentally poured that gallon of water into your cereal so you can safely laugh away that mistake. When we do stupid things online, however, they are there for everybody to see.
Reputation truly matters when it comes to the job search. That profanity-laced post you wrote about your ex-boss probably seemed hilarious at the time, but it will cost you if it's ever seen by potential employers. It's easy enough to delete the post but that won't permanently solve the problem. Links to deleted posts will still appear in search engines for a short while. Even though the link won't work anymore, that won't help you much if the title of your post is embarrassing.
There are reputation defending services that can help you with this, but they don't come cheap. The best remaining option to clean up your online reputation is to create new content to drown out the bad. Update your blog with new content that shows your professionalism. If you publish enough new material, those posts will be easier to find then your more questionable articles.
One thing to keep in mind: Don't write too many posts in one day. How much is too much? A good rule of thumb is to stop writing when you run out of interesting and relevant things to say. Rambling posts that have no coherent train of thought can do as much harm as profane ones.
Your blog doesn't have to be your only source of written material. There are literally hundreds of article writing sites out there that will help get your name into search engines. Use them to publish articles you have written offline or write new material. This will serve the dual purpose of getting your name out and enhancing your efforts to bury reputation-damaging material.
Of course, the best way to avoid hurting your online reputation is to avoid writing unprofessional things in the first place. Think before you write!