Search inside the text of Word docs, PDFs, PowerPoints, Excel files, etc.
The search feature should pull results from inside attachments, like Outlook currently does. This is invaluable when files are frequently labeled poorly. Also, allowing you to choose to only search attachments would add a lot of value.
For example, a search for a company name that might be in the signature line of a legal document, but not in the file name would still allow you to find the document you were looking for.