I understand your point about leaving a tip, but I don't understand what you mean when you say it takes longer than with a pen and paper.
As far as the tipping, I can see this as being one possible solution. How about a calculator of sorts being built into the system. Maybe on the screen there is a small number pad. This pad is labeled clearly TIP CALCULATOR.
Three buttons on top of the number pad read "Tip By Percentage" and "Tip by Dollar Amount", and "Bill Total". If you want to tip by percentage, you hit that button, then you just punch 18 for 18% and it is automatically added to your total. If you want to tip by a specific dollar amount, you hit that button and then you punch in the amount that you would like to tip, and it is added to your total, or finally, you use the "Bill Total" to simply state what you would like to pay in total with the tip included. The system would then just back the tip out of that total for the server's record keeping purposes.
This may sound complicated, but this is the direction in which our world is moving. People are still intimidated by the self checkout line at the grocery store, but others such as myself could not live without it. What about when the "slide your own debit/credit card" terminals first came out in the checkout lines at places like drug stores and gas stations. Was it really that big of a deal learning how to use it? It took most of us one time, although many are actually a little different, it is still no biggie.
Same thing with this sort of technology. It will be forever evolving. People will soon be forced to start thinking very differently about many things that we may now consider trivial. Technology is evolving on a scale that literally makes the "must haves" of three or four years ago completely obsolete today.
When Bill said he is building an empire here, one has to be intrigued by the possibilities, especially with the chance to be one of the first to penetrate the U.S. market. This thing is still in its infancy. Many are just here to make a quick 5 or 10 Gs. Good for you, but realize there is much more potential here than just a penny stock that may trade for a couple of nickels in five years. Much more here to be had.
I have said it before and I still believe that you could wait a couple of years to get in on this and still get rich, not because it is going nowhere fast, but because the potential for sustained growth over many many years here is astonishing.
