When I was a child, everyone received Communion on the tongue. (Many churches still allowed you to kneel, when receiving.)
A number of years later, this would change. In fact, I remember very vividly the arguement put forth was "This is a more adult way of receiving Christ."
Now, at the time, I kept attempting to find arguements to refute this, but could not. The wave of this change was unstoppable.
Over the years, I think that I have recieved Holy Communion only once or twice in the hand. To this day, I continue to receive it on the tongue.
Over the years, I have watched people receive Communion to see if they are doing it correctly (yes, I know, I should have been focusing on the mystery of it).
When going up, some bow, a couple have knelt, some make the sign of the cross, and some are who knows where.
Of course, there seem to be mutiple ways to receive it: left hand flat out with the right hand under it, right hand with the left under it, both hands out side to side.
Finally, you may put it in your mouth with your fingers or just pop it in, like an M&M.
Aufer a Nobis has some thoughts on this.
Personally, I think he is on the mark and I would love to see a return to Communion on the tongue.