I'm making a game and I believe it's going to be pretty innovative. Should I keep a public development blog, or should I just write something about the progress in private, for the sake of someone not copying me. Don't get me wrong, I'm all for the open source and free software, but I'd like to finish my game first and then see people come up with similar ideas.
You'll hear from a lot of people that ideas are worthless. Execution and passion are what matter.
There are a lot of good reasons to run a public development blog.
But there are also some bad ones
Worrying about somebody "stealing your idea" isn't worth it. Once your game is finished, if it's any good, somebody's going to borrow from it. Even if it's an unabashed rip off they may do a better job than you can. The only thing hiding your idea gives you is a theoretical head start. It's better to just release something good and give it to an audience that wants it than trying to hide it away.
But at the end of the day you have to ask yourself why you'd want to start a blog. Can you actually pull off what you think you want to do? Are you focusing on the product itself or are you thinking a bit more ahead about what happens after the product is finished (either by shipping or getting shelved)?
I maintain a blog for my game, and I did wonder this same thing in the beginning. Although I wouldn't call my game original, there isn't another game just like it. Like many games (or even ideas in general), it's built on the shoulders of the giants before. It's all about how you implement your idea, not the idea its self. No one will be able to implement the idea like you can, especially since it's your idea and only you know all the details. If you're in development for the joy of making your ideas a reality, I think you'll find maintaining a blog very rewarding.
I find that blogging about features as I add them really makes me understand the features better. It's fun to get feedback about the game as you're making it. When people say how cool your game looks or that they want to play it, it really motivates you. Good luck!