We have been using Symantec EnterpriseVault (EV) for a few years now and it works very well for us. There are two dedicated servers that handle the journaling and the archiving to our Centera. We grew from four 75 GB stores for a few hundred emplouyees to now, where EV has about 7 TB archived on our Centera & Exchange has around 2.7 TB total in all our active stores. The solution grew with us and we will probably begin using its File Services archiving soon, too.
We have explored using EmailXtender in conjunction with DiskXtender when we move to exchange. But dont use any tool rt now since our current mail application is not supported.