One of the biggest complaints I see developers raising about SSIS since it was released in 2005 is that the only way to debug Script Components is the distinctly simplistic and old fashioned method of sticking up message boxes - there is no way to step through the code as it executes (something that Microsoft developers have generally been able to do for eons).
Happily that is no longer the case, or won't be soon anyway. In his session yesterday at the PASS Summit SSIS team member Matt Masson revealed that proper Script Component debugging (breakpoints, step into, step over, etc...) will be coming to SSIS 2012. Matt asked me to point out that nothing is certain, things may change before RTM blah blah blah but ostensibly SSIS developers can now sleep easy in the knowledge that message box debugging has gone away forever. Great news!