How many?

Someone tell me just build for 3 -4 backlinks / day is good, and to avoid penantize from google.

That's true?

If true, how to limit with "natural" backlink?

 

You can build a lot more than that a day and it'll be fine.

 

This mean the "Google Penantizing" is joke?

 

I doubt it's a joke. I think google is smart enough to figure out if links are natural or not. If you get hundreds of spammng looking links a day than yes you will probably eventually get penalized but if you get hundreds of natural links you will be fine.

 

It's not a joke
But don't exagerate few k's or 500+ links will raise flags

 

/ day or / month?

 

I think you can safely add 100-200 links a day without getting into any trouble with Google. When people get to the front page at Digg they get massive links in a short period of time and Google has no problem at all. Unless you are doing some kind of link spamming thousands of links daily I wouldn't worry.