I was doing some investigating on PHP.net and read that array_flip(array_flip()) was faster than array_unique() for integers.
So I did a test, and found it to be so.
I happened to have a list of 750,000 URLs (strings!) in an array, of which many were duplicates (50,000 unique).
I threw it in a test and got some interesting results:
$start1 = microtime_float();
When saving the results to files, they were identical.
I know the difference isn't amazing what happens if there is (int)1 and "1" as variables in the array and what happens (too lazy to test today) and probably a number of other things but I found it interesting.
Also it only works if the contents are strings and integers. (PHP very clearly shouts that at you)
Warning: array_flip(): Can only flip STRING and INTEGER values!
Fun fact of the day!