[Ken Case]

The "OmniFocus: Send to Inbox" Service should appear in the service menu of an application once you've run OmniFocus at least once, then restarted the application. (Unfortunately, applications don't notice changes to the service immediately, so you have to restart them to get them to notice the new service, or to notice changes to it such as a newly assigned keyboard shortcut.)

Check OmniWeb's Services submenu inside the OmniWeb menu. Do you see "OmniFocus: Send to Inbox" listed as a service? Is it enabled when you have text selected on a page? Does it work when you select it from the menu?