Last week Roel had a posting about jQuery's Date Picker: http://roelhartman.blogspot.com/2008/12/how-to-replace-default-apex-calendar.html Definitely a great example for people who are looking for an alternative to APEX's date picker.
We do use the jQuery calendar and have some interesting standards around it (I'll try to blog about this another day). The most important one, and easiest to implement, is the date format standards.
We have 2 application level items:
F_DATE_FORMAT: is used for the application level date format
F_JQUERY_DATE_FORMAT: format to display the date the same as f_date_format
Both these items are set at login time and the values are defined in our database at the client level. You have to make sure that the date formats produce the same results.
In Roel's example he uses the jQuery on load function. For the date format just use &F_JQUERY_DATE_FORMAT. instead and this will load set the jQuery date formats accordingly.
Here's a listing of jQuery's date formats: http://docs.jquery.com/UI/Datepicker/%24.datepicker.formatDate
And Oracle's date formats: http://www.techonthenet.com/oracle/functions/to_date.php
Hope this helps,