One of the best features of Dynamics CRM is the integration to Microsoft Outlook. In comparisson to competing CRM systems, this is really one of the strongest unique selling points of Dynamics CRM.
However, even though it is really good, there are some parts of it that could use some touchups and until that happens, some workarounds would be good.
One of these issues, is that appointments can easily be created from Outlook and mapped to some object in CRM. This is easy and very few click. Nice. But, when this appointment is completed, it is a bit more complex and a lot more clicky. First you have to open the appointment in Outlook, then open the appointment in the CRM form. From there, you can press the "Save as completed" button, which is a bit tedious and many users find this a bit strange and I am having a hard time explaining why you have to do it this way, it isn't very obvious or logical. The best solution would be that the CRM addin had a button which could mark appointments and other activities as completed. But that just isn't there yet.
So, is there a workaround, yes, of course there is. It isn't perfect, but it will work.
Define some text, like for instance "Completed" and then tell the users to put Completed as the last text in the description field or in the subject field.
Then create a workflow in CRM that triggers for updates on the field where you expect the text. Then let the workflow check if the end of the content of that field is "Completed" and if so, set the appointment as completed.
The same functionality could of course be implemented in a plugin instead, but that requires a bit more programmatic skills.
The functionality of adding a button to Outlook can of course also be developed with Visual Studio Tools for Office (VSTO), and that could of course be used to automatically update the appointment as completed.
So, that might help you out a but I really hope that the CRM Client for version 5 will deliver this functionality since it isn't very hard to do when the rest is there.
Microsoft Dynamics CRM Chief Architect