When you tap the Send to OmniFocus link, it should launch OmniFocus (if not already running), switch to OmniFocus, and put you in the Quick Entry dialog, with the subject line of the message as the action name and the body of the message in the notes field. If you tap and hold on the link, you should get a popup showing you the value of the link and asking if you want to Open or Copy. If you get that, and tapping Open there still doesn't do anything, then it sounds like the omnifocus: link handler isn't correct. Have you ever had the iPhone version of OmniFocus installed on your iPad?
You might try reinstalling OmniFocus and restarting your iPad, but be sure that you are either syncing your database with another device or the Omni Sync Server so that you can easily reinstall the database! Or you can go to the Apps tab in iTunes, scroll to the bottom, select OmniFocus and save its OmniFocus.ofocus file to your Mac so you can put it back via the same route. If you aren't 100% sure of what you are doing and you are only running OmniFocus on the iPad, it might be prudent to call Omni support on Monday and have them walk you through the process (and they may well know of some other way to fix this): 1-800-315-OMNI or +1-206-523-4152 rather than risk losing your data. Personally, I think it is a good idea to sync with the Omni Sync Server even if you don't have any other devices or the Mac client, just for the automatic backup it provides you!