Alan Pelz-Sharpe has a great post on the CMS Watch Trend Watch blog that describes the difference between back up and archiving (they are not the same). He makes the point more articulately than I ever could so I will encourage you to click through. Alan goes on to say:
2008 will see ECM vendors aggressively trying to move into the archiving sector. It's a move driven (as all meaningful market dynamics are) by buyer demand. At the moment, demand stems less from a full understanding of retention and archiving, and more from the need to shift ballooning volumes of e-mails (e-mails that may well become the focus of a laywer at some future date), that are swamping mail servers.
If ECM vendors respond to the stated need of handling larger volumes of data, I doubt that their solutions will address the core need of organizing and filtering information into a useful archive. Are we talking about bigger refrigerator doors? In the case of email, will their solutions be smart enough not to "archive" marketing, personal, and other email with no legal value?