The Value property is a string that the ToolTip can hold and it is useful for passing information that is necessary to the application logic down to the user control that is loaded in the tooltip, for example. You can see it in action in the following demo: http://demos.telerik.com/aspnet-ajax/tooltip/examples/targetcontrolsandajax/defaultcs.aspx
. Please examine the RadGrid1_ItemDataBound method where the Value is set to the ProductID of the target control (in the ToolTIpManager's Add method) and then the UpdateToolTip method where this information is passed to the user control for its databinding.
When you install the Telerik RadControls for ASP.NET AJAX you also get the Live Demos installed locally (in the Live Demos folder in your installation directory) so you can inspect and modify their code freely. The webservice code is there as well in the App_Code folder, the ToolTipWebService.cs file.
The way to use a webservice is shown in the demos while the actual webservice is not shown since it is a custom function that is not relevant to the RadToolTipManager.
As for the documentation - it is indeed a little outdated and we are currently in the process of updating it, but I cannot provide a firm estimate as to when this task will be completed.
the Telerik team