Microsoft released a tool with Office 2013 called the Discovery and Risk Assessment tool that helps your IT organization find spreadsheets that are overly complex and risky. It uses a risk matrix that ranks your spreadsheets based on complexity of formulas, the number of sheets, the number of external connections and cross linking of workbooks.
Microsoft has just announced that this feature will be moving into the eDiscovery Center in Office 365.
Using a set of configurable search criteria, you can now add finding spreadsheets to your eDiscovery rules and track down overgrown spreadsheets based on a number of items and complexity of workbooks. As part of the eDiscovery Center, you can then also set rules on what do with found items, e.g. notify people, place a legal hold on the files, export the results, etc.