Hi David,
If all else fails you can cast the UserControl as mojoRating in code and set the property. UserControls are difficult to use across projects in a strongly typed manner but you can set properties declaratively. I use it in WebStore project and bind it in a repeater in the product list like this:
<portal:mojoRating runat="server" ID="Rating" ContentGuid='<%# Eval("Guid") %>' Visible='<%# (EnableRatings && Convert.ToBoolean(Eval("EnableRating"))) %>' AllowFeedback='<%# EnableRatingComments %>' ShowPrompt="true" PromptText='<%# Resources.WebStoreResources.RatingPrompt %>' />
I'm really not very happy with the implementation of the mojoRating control, it renders too much javascript into the page, really its the AjaxToolkit rating control that does this, at some point I'm going to find a better implementation.
Adding this to the <pages><controls> section of your project's Web.config and adding a reference to mojoPortal.Web may or may not help
<add tagPrefix="portal" tagName="mojoRating" src="~/Controls/mojoRating.ascx" />
Best,
Joe