Currently you can use your own objects which need to implement the IGanttTask interface which is also in the GanttView assembly. We are planning to add data mapping feature which will allow you to use arbitrary objects and just to specify property mappings for the properties we need like Title, Start, End, etc.
This feature is planned for the 2012 Q2 SP1 release so it should be developed shortly after the Q2 release at the middle of June. Hope this time frame is OK for you.
All the best,
the Telerik team
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