Working with Dynamic entities is a bit different in 4.0 vs. 3.0.  When writing plug-ins and using Microsoft.Crm.Sdk, you have the ability to access the attributes of a Dynamic Entity via a property bag, much like this:
DynamicEntity updateEntity = new DynamicEntity("m3_roundrobin");
updateEntity["m3_lastuserid"] = newOwner.ToString();
updateEntity["m3_teamid"] = teamId.ToString();
However, if you're writing an application that used the standard CRM [...]