We're not aware of any Mac related issues, so I'd ask you to send us more details on the exact setup of the customer ( Mac OS version, used browser, etc) as well as on the application. We have tested loading many appointments in the control, but did not manage to observe the described performance issue. If you could provide us with some sample code, it would be of great help.
Note that without researching the case further, we cannot specify whether there will be performance improvements in Silverlight 5.
I am looking forward to your reply.
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