With the arsenal 37Signals provides, why would any company use Yammer? I found it as useful as Google Wave. Seriously, it could sort-of replace email if everyon

With the arsenal 37Signals provides, why would any company use Yammer? I found it as useful as Google Wave. Seriously, it could sort-of replace email if everyone in a company used it, and if Dropbox didn't exist...and of course Basecamp had never been dreamed up.