Hi Roddy.
Yes, we have our Decision Logs in Clarity. It is a simple sub object of the project object (sub object screen shot below - feel free to do what you need with your thing). We find this works really well. The advantage here is, because of the project association, it's real easy for us to view this information by Project, Project Manager, Program, Portfolio, OBS, etc (portlet screen shot below). Clarity's ability to aggregate, search and 'slice & dice' like this is something that simply can't be done in Excel or with SharePoint lists. The project association also allows you to (optionally) enforce any security/visibility business rules on the decisions that you have on your projects. If this control is important to your organization, this is another thing that the other tools just can't touch (without the work of rebuilding your Clarity security model in the other tools). We think a Decision Log object like this in Clarity is one of the easiest 'wins' you can create for your organization.
Let me temper this - it's notsomuch about the DL object and portlet, the value is obtained through your business process and usage. We have a codified, documented DL process that makes this work. You should too.
HTH,
Rob
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