[Richard Flynn]

The problem is not OmniFocus’s, but Apple’s. Apple designed the Services only to work effectively when text is selected in a Cocoa application. But all is not lost! The Omni Group have come up with a little plugin for Mail which, when a message is selected, it makes the Services believe that a piece of text is selected and behave accordingly. To install this plugin, go to OmniFocus preferences, choose the Clippings tab, and at the bottom is the option to install their ‘Mail Clip-O-Tron 3000’ plugin. Once the plugin is installed, you can select a message within Mail and choose the ‘OmniFocus: Send to Inbox’ item from the Services menu, or press your OmniFocus Clippings Shortcut (as defined in the Clippings tab of OmniFocus preferences). (You’ll have to close and re-start Mail to see the effect.)

I’m afraid something similar hasn’t (yet?) been done for Safari.

The benefits of this system over the iGTD system is that this is using a system-wide Service which will thus work in all Cocoa applications on your machine. The downside, as you have already seen, is that there are some limiting factors to the Services as provided by Apple. I understand (from earlier forum posts) that the Omni Group have been discussing this whole matter with Apple, so we can only hope that Apple will listen and will make the OS X Services slightly more flexible.