Just upgraded to Mathematica 8.0.4 Student Edition under Linux. Seems like there exists a bug in scripts installed (under target installation directory) as Executables/Mathematica and Executables/mathematica. Namely, file template for mktemp command in line 202 of these scripts has only five 'X' characters at the end, instead of six. Because of this, corresponding temporary file is not created, and Mathematica is unable to use any fonts, so it won't start. After adding an additional 'X' character in the template, Mathematica would start normally.
(Note: I'm using Slackware64 13.37.)