Squirrel SQL 3.5.1, Ubuntu 12.10, Java 7, PostgreSQL 9.1:
Exporting date/time values to XLSX results in completely wrong values. The exported cell format is numeric (instead of the expected date or time cell) and contains a localized numeric values instead of the date.
a TIMESTAMP of "26.02.2010 12:04:59" (German date/time format) will be exported to XLSX as "40235,5451273148" (German number format).
Export setting was "Use formatting as configured in Global Prefs".