Having the same problem as well, but the only thing that's worked has been deactiviating all my fonts except the system fonts... that said, doing this has left some web pages looking a little clunky. Like many others I've read about with this problem, I have a third-party font manager installed, FontExplorer X Pro 3.
One thing different for me though, Google Chrome was completely broken at first along with Safari - showing an "Awww shucks..." error. I had changed the default font for both Safari and Chrome though, and Chrome was already having font display issues under Snow Leopard because of FontExplorer X. Deactivating everything but system fonts got it running again, again looking a little clunky though.
Hopefully someone can find a permanent fix... and I do wonder if I'm missing new Lion fonts or older fonts after the upgrade to Lion - fonts that FontExplorer X blocked or deleted somehow. ON my first startup FontExplorer showed some missing system fonts but those warnings later vanished.
A restore of Snow Leopard and reinstall of Lion without FontExplorer may be an option to consider.