I'm looking to find the object types of the WhatId/WhoId fields of the Task and Event objects, so I can query these objects and get more information about them and perform certain automated tasks based on the type.

I found this tech article, which uses the first 3 digits as a marker, but the article also says that this may change at any time:

http://www.sforce.com/us/resources/tn-1.jsp

Is there a better way of getting the object types of WhatId/WhoId fields or querying them based on Id only (no type)?

Thanks!