It is important for your mental health to take short "breaks" occasionally. Most people tend to find it difficult to concentrate intensely on one thing for more than 20-30 minutes, so after a brief bout of "deep thought", it's actually good to shift your focus to something completely unrelated. Even better is to stand up, stretch the legs, and walk about for a minute, which is also good for maintaining your physical health if you're stuck behind a desk all day.
In a relaxed working environment this is easier to do. If your boss is a real B***D and frowns on anything that keeps you healthy during your work hours, then this is something to either negotiate, or to do discretely. As long as you are getting your work done and meeting your obligations, taking occasional short breaks should not be a problem.
However, if you are sitting around playing games, updating your blog and other stuff, then you are probably on very dodgy grounds ethically. If you are meant to be working, but instead simply taking time out to essentially screw around, then you'll end up with a poor performance review, and possibly being shown the door.
The line between how unprofessional or not your behaviour is viewed will come down largely to company culture and your relationship with your boss, but will also depend on how you go about taking your breaks, and your reasoning why.