I ran into a problem installing Lion on my Mac Pro. The install screen appeared to be stuck at 33 minutes with no sign of progress. Several reboots later and still no luck, I noticed that there were a lot of disk errors in the install log that appeared to stop the installer in it’s tracks. It appears the installer doesn’t validate your hard disk before installing and is unable to report failures when encountered. So before installing, run ‘Disk Utility’ and save yourself the three hours I wasted. If you do reach this point and there’s no sign of progress. You can still boot back into Snow Leopard by selecting ‘startup disk’ from the Installer’s menus.