That's the pressure that a group of scientists believe will take hydrogen fuel cell vehicles to the next level. The team argues that storage units designed to hold hydrogen at 10,000 psi are quite expensive and claims the moderate 500 psi is far more practical.
In the online issue of Journal of Physical Chemistry Letters, a group of scientists published a paper titled, "Hydrogen Spillover Effect of Pt-Doped Activated Carbon Studied by Inelastic Neutron Scattering." Omitting most of the technical details (which you can get here if you have the right credentials), the team's paper concludes that a vessel lined with activated carbon with platinum would allow hydrogen to be safely stored at 500 psi.
According to the team's paper, 500-psi storage tanks could, at least in theory, cost less than tanks engineered that need to withstand 10,000 psi. But there's one major issue before we're all cruising around with "low" pressure H2 tanks under our seats: they require platinum, one of the world's most expensive materials.