A question was asked on the SSIS forum about conditional execution. The questioner had a data-flow that checked some incoming values and, depending on cetain characteristics, could identify that row as being "bad". (S)he then wanted to do some action (in this case send a mail) if the number of bad rows exceeded 0.
Conditional execution is what is needed to accomplish this - namely expressions on our precedence constaints. The steps are to:
1) Use the rowcount component to capture the number of bad rows
2) Populate a variable with the number of bad rows
3) Check the value of a the variable in a precedence constraint. if it is greater than 0, do the action.
I have put together a little demo of this that may prove useful. I have used a script task to display a message box for the "action" rather than sending a mail. It can be downloaded from here: http://blogs.conchango.com/Admin/ImageGallery/blogs.conchango.com/jamie.thomson/20050725ConditionalExecution.zip.
-Jamie