We all know about the issue of high level characters being able to jump from infinite heights without fear of dying. There have been many solutions proposed, some more complex and some less so. I believe, however, that there is a very simple solution to falling damage... increase the size of the damage dice. Increasing falling damage die size from d6 to d12 will go a long way towards making falling more dangerous. It is even possible to increase damage dice to d20, though that would be a bit non-standard and in any case the d12 does not get enough use!
On another note, we could either remove the damage cap of 20 dice or make characters take double damage from falls if they fail their Jump/Tumble/Acrobatics (however the skills end up in the final version of PFRPG) checks (or even do both). We could make the DC for the check something like: 0 + 1 for 10 feet fallen.