For All Intensive Purposes

From Encyclopedia Of Stupid

For all intensive purposes is stupid, and so is anyone who says it.

This is another example of stupidese, a dialect of English commonly used by 99% of assholes, or anyone educated in the American Public School System.

The correct usage is For all intents and purposes.

Or, as described in Common Errors In English Usage by Paul Brians:

Another example of the oral transformation of language by people who don’t read much. "For all intents and purposes" is an old cliché which won’t thrill anyone, but using the mistaken alternative is likely to elicit guffaws.