Yes.
Also, we contacted the author of the SalesForce Zimlet directly to
try to determine what is required on the Salesforce.com-side for you to
use the zimlet (Zimbra extension/plug-in).
He informed us that each SalesForce.com account must be licensed
with the Enterprise, Unlimited or Developer SalesForce products, and
must be given permission to use the APEX API interface. The SalesForce
web site is unclear as to the specifics of what must be configured
per-account beyond having an Enterprise license.
We have tested the SalesForce.com Zimlet successfully in Zimbra 4.0.x, 4.5.x and 5.0.x.
We have another article in our blog here on using the SalesForce.com Zimlet from within the Zimbra environment:
http://blog.01.com/?p=143