Read the transcript for the McD Q4 earnings call and it was mentioned they had just completed a 60 million dollar cost reduction program. So I don't think they are kidding about the extra 250-300 million dollars in cost savings they want to extract after the merger is complete (especially when they expect a one time charge of 200 mln).
If you're in a role that is duplicated I would probably start looking for something else, if you are in a business group that has no work time to start looking, if you are in a group that has had a lot of project performance issues I would start to look. Probably no different than if the company were going to go BK.
I heard when Dave visited the Dubai and Khobar offices he told people there that they should expect job reductions because there were too many people. Probably gives you a flavor of what might be heading down the line.