Hi Tim -
If I modify the date format in the admin setting section:
http://<site-url>/admin/settings#tab-formats -> Date and set it to something like '%d %b %Y' the site crashes.
I've found out that this is caused by a null reference in app/helpers/application_helper.rb in
datepicker_format where it tries to downcase date_format (which is undefined in case the date format contains anything other than the three replacements %Y, %m and %d).
I'm not sure what the return value of datepicker_format is used for so I could not figure out the best resolution.