Unfortunately the Forums module is limited when it comes to functionalities like this one. While the News and Blogs items has view count, which are metafields, the Forums module does not. It is not based on the Generic Content architecture, and the metafields approach would not work for it.
We will provide this functionality in Sitefinity 4.0 though.
Don't hesitate to contact us if you have other questions.
the Telerik team
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