I recently played with Ubuntu and Google Chrome to check out possibly greener pastures, and coming back to OS X and Omniweb is bliss :-)
So I really wanted to solve this issue. TimmyDee pointed at an issue that
bugged me and others at the introduction of Snow Leo. At that time I had changed my keyboard short cut settings regarding dictionary lookups not to interfere with Omniweb's direct bookmark feature. That's what bit me now that Omniweb's behavior had changed. Sadly that wasn't mentioned in the release notes. That would have helped a lot.
So to resolve my issue I had to change my custom Dictionary lookup short cut again and delete my former Omniweb override short cut.
Thanks for the suggestions guys and maybe this helps someone in the future.