A simple illustrative script which copies any lines currently highlighted in a Mail message, and places them in the Omnifocus inbox as separate tasks.

Might partially fill a gap until Omni writes a Clip to Inbox service.

I assume it might also be feasible to write a QuickSilver action (for use in conjunction with Apple-Esc to capture the selection) which sends the selection line by line as separate tasks to the Inbox.