I only use double-tapping for 1 frame links/link combos. Though, I thought double-tapping for strict links came naturally to some people? I learned it as I figured it increased my chances of hitting links in 3s and some of the challenges in 4.
The only problem I see is that once you rely on double/triple tapping, you might get into the habit of doing it too often when it isn’t needed. 
I know this is thread about the double tap but this little trick probably belongs here. It certainly doesn’t need a whole thread for it.
I forget how known this technique is but its pretty uncommon. This came to me one day when I was thinking about if I could improve the piano technique. so with 3 fingers, you can piano and get 6 inputs. However with a different technique, you can actually use the same 3 fingers and get 18 inputs. This method is not a piano style. Its more of swipe\drag.
- Learn the distance between your buttons like this.
http://www.imagechicken.com/viewpic.php?p=1263378714047045100&x=jpg"%20target="_newwin"><img%20src="http://www.imagechicken.com/uploads/tn1263378714047045100.jpg"%20border="0"%20title="Free%20Image%20Hosting"%20alt="Free%20Image%20Hosting
- Once you figure out the spacing, position your hand outside the buttons.
http://www.imagechicken.com/viewpic.php?p=1263379195099307200&x=jpg"%20target="_newwin"><img%20src="http://www.imagechicken.com/uploads/tn1263379195099307200.jpg"%20border="0"%20title="Free%20Image%20Hosting"%20alt="Free%20Image%20Hosting
- Drag your fingers over the row of p OR k. I messed up on my diagrams a little. Remember that you choose the ROW of p\k. I accidently have the technique covering up both p\k rows.
http://www.imagechicken.com/viewpic.php?p=1263379269047698100&x=jpg"%20target="_newwin"><img%20src="http://www.imagechicken.com/uploads/tn1263379269047698100.jpg"%20border="0"%20title="Free%20Image%20Hosting"%20alt="Free%20Image%20Hosting
- continue dragging
http://www.imagechicken.com/viewpic.php?p=1263379821067830700&x=jpg" target="_newwin"><img src=“http://www.imagechicken.com/uploads/tn1263379821067830700.jpg” border=“0” title=“Free Image Hosting” alt=“Free Image Hosting”
- continue dragging
http://www.imagechicken.com/viewcode.php?p=1263380792005285900&x=jpg
- eventually your hand makes it all the way to the end.
http://www.imagechicken.com/viewpic.php?p=1263379542043368800&x=jpg"%20target="_newwin"><img%20src="http://www.imagechicken.com/uploads/tn1263379542043368800.jpg"%20border="0"%20title="Free%20Image%20Hosting"%20alt="Free%20Image%20Hosting"
You can actually piano with 1 finger if you drag it. This is the difference in the methods between the piano and drag. I practiced this for a while and got pretty fast @ it, but the ability to move your hand outside like that mid game is actually sorta slow. Its much easier to just piano than do this. Kinda impractical @ the moment for me. My games don’t require something like this but I still think its pretty cool.
To my knowledge, this is the max input speed for a human being. Anything faster than this is PPAD timing IMO. I can’t think of another technique that will allow that many inputs just as fast. You can perform the drag just as fast as a piano. Granted that when you do it fast it can be screwed up but the # of inputs you get exceeds 6 all the time. You’ll probably average over 12 easily. Hitting all them perfectly to gain 18 consistently can be quite challenging mid game.