From Facebook Developer Wiki

In regards to the integer prop_type, right now there are the 3 types:

   1 for integer
   2 for string (max. 255 characters)
   3 for text blob (max. 64kb)

how about a forth for storing date & time?

You can store a date and time values as either an integer (e.g., number of seconds since 1970) or a string (e.g., “7/21/80 12:32:12”). Is there a reason you'd need a native date/time type? --Pete (563683308 22:39, 3 December 2008 (PST))

There appears to be a limitation on the property name such that it can't be one of the names used internally such as "oid" or "type". I had a object type that contained a "string" property "type" and received 803 errors when trying to retrieve objects by object id. --Johnny (44406202 18:47, 6 September 2009 (PDT))