I recently upgraded jetpack to version 1.8.1 and Google Analyticor 6.3.4. Immediately my site started reporting 500 internal server errors on the user side, but not the admin side. I use the FavePersonal theme from CrowdFavorite, based on their Carrington framework.
If I deactivate either plugin, the site works.
If I switch to TwentyEleven theme, the site works.
Most importantly, if I turn off the Google Analytics admin dashboard widget, the site works.
PHP did not generate any error_log entries for the 500 errors.