Dude, you must be reading my mind, 'cause I just signed in to post the thread about this technique, and I see your message, lol.
Anyway, it has been called many things in the past, most recently it has been called the instant double jump. I'm just gonna call it the boost jump for right now. The boost jump varies drastically from char. to char., but for Ike in particular, it allows him to perform his aerials with little to no landing lag. But there is a cost, you lose a jump. But when you think about it, you're giving the second jump to boost the first one.
This is how you do it (well, this is how I do it):
Tap Jump then immediately press Y for an empty boost jump.
Tap Jump, imm. press Y and buffer the c-stick for boost jump aerials
The boost jump also looks different from the double jump and normal jump in 2 ways:
first - empty boost jumps have dj rings on the ground and boost jump aerials have no dj rings
second - most characters boost jumps fall between the short hop and full hop in terms of height. There are exceptions though. Quite a few. So yeah I don't have any vids right now but I'm about to post this info and see what happens. er. . . on second thought, I better wait. I might post this with the boost fall and my buffered aerial research. Sorry about the wall of text.