The phrase that I emphasized in the paragraph below, found on this page that describes possible problems with updating to 2009, can be interpreted as euphemism:
Previously, InstallShield did not contain support for compressing files that were streamed to the Setup.exe file or the ISSetup.dll file during assembly. Thus, if you compare the release that was built into InstallShield 2008 or earlier with the same version that was built with the default compression level in InstallShield 2009, you may notice that the size of the Setup.exe or ISSetup.dll file is slightly different. In addition, the time required to extract the files may vary slightly .
IS2009, , , ?