>My report contains several data fields that are populated by UDFs. These UDFs return a number that requires a fair amount of processing. I would like to set the PRINT WHEN to not print when the returned number is zero. However if I put the expression MYUDF()>0 in the PRINT WHEN box I will be forcing the report to run the UDF a second time to determine if the control should be printed. This will slow down the execution of the report considerably as the table size grows ever larger.
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>Is there a way to tell the report to not print the control if the value is zero without running the UDF again?

First, try to set the format of those report fields to "Blank if Zero". If it doesn't work for you, move all those calculations to the report variables. After that you can use such variable in the field expression and PRINT WHEN.