"Zimbra says that since all Google docs and files are stored on Google's servers, public companies would face big Sarbanes-Oxley compliance issues if they deployed Google Apps. The solution? You guessed, it: deploy Zimbra instead. Zimbra told R/WW that their messaging and collaboration platform 'provides enterprise customers with freedoms that Google Apps just can't provide, including the ability to archive for compliance purposes.'"
Its a good point, but I think the compliance gap is a lot easier for Google or another Office 2.0 contender to fill than the mashing gap I also mentioned.