Update (2012-08-02): Visit http://icalfilter.com/fbfix.php and paste the url to get the url for the corrected calendar.
When exporting your Facebook Events feed to webcal/ical/ics, the whole day (no given time) events are one day early. Until Facebook decides to fix this, I have created a proxy script. Just supply it with the same uid and key as in Facebook's version and it will correct these errornous events.
It works like a charm for me, but let me know if you are having trouble using it. Also check out http://icalfilter.com and see if it might be something for you as well.