I was just running a report that was supposed to include all accounts with a specific date field of On or Before 12/31/12. I realized after comparing it to an identical report in Salesforce that it was including accounts where that date field is blank. When I added a start date (so between 1/1/2009 and 12/31/2012) it fixed the problem. I contacted support and they told me this was "expected behavior". That seems strange to me. On or Before Date should exclude blanks. This is the way Salesforce does it and seems to be the more logical choice.
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