Clipping material from other applications
You may come across an email message, a web page, a newsreader article, or some other scrap of info that you’d like to turn into an OmniFocus action. In the olden days you might heft your mouse, highlight the text, copy it, summon up the OmniFocus quick entry window, and paste. But no, you’re living in the future. You use the OmniFocus Clippings service.
To clip content from another application:
Highlight some text in any application (that is, any application that supports Mac OS X Services, which should be all applications these days, ahem). 
Press the Clipping keyboard shortcut (Command-Shift-Option-Period by default), or open the application menu and then the Services submenu, then choose OmniFocus: Send to Inbox.
A new item, with the highlighted content (rich text and embedded images) as its note, lands in the quick entry window for you to revise and save. 
You can change some details of how clippings work with the OmniFocus Clippings preferences. From the OmniFocus menu, choose Preferences, then click the Clippings tab.
To change the Clippings Shortcut, click in the field and type a key combination. To clear the shortcut, click the X button.
With the Copy Clippings to setting, you can choose whether to clip material into the quick entry window for review and revision, or to drop it straight into the Inbox.
OmniFocus processes material differently depending on which application it was clipped from, using application-specific plug-ins. For example, when you clip content from Mail in Mac OS X 10.5, the new action has the message’s subject line as a title, and its note has a link to the original message. You can select an application in the plug-in list to see details about how it will process clipped content. You can also turn off plug-ins you don’t intend to use, or for which you’d rather use the “Any Application” plug-in.
The OmniFocus Mail Clip-O-Tron 3000 is a little tool that adds the ability to clip the entirety of the selected message in the Mail message list. To install it, open the Clippings preferences and then click the button in the lower-right corner. If you don’t install it, you can still clip content highlighted in Mail’s message content area.