Microsoft Dynamics CRM 2013 introduces Server-Side Synchronization. This provides an alternative to using the Email Router and the CRM Client for Outlook.
A key advantage of Server-Side Synchronization is that processing of emails is performed by the Asynchronous processing service so there is no need to install the Email Router. However, Server-Side Synchronization is not available in Microsoft Dynamics CRM Online Fall 2013; which is disappointing because having to install the Email Router detracts from an otherwise completely cloud-based solution.
I suspect that Server-Side Synchronization will be made available for Microsoft Dynamics CRM Online in due course (perhaps in the Leo release?).