After those, None what so ever.
They are the most public face of the team however (apart from maybe the team principles, but a lot more people could name Hamilton and Vettel than Witmarsh and Horner no doubt). So they have a important 'setting the tone' in terms of feel and in confidence.
But as the actual mechanics and engineering?? Not much at all beyond feel and setup.
Edit: It does amuse me all the doom mongers and naysayers maybe starting to do a little backtrack. Things change, and things improve or decline. I've never said that Merc would be world beaters out of the box, but likewise all those which automatically have written them off (and theres been a lot), might have been a bit premature.
Edited by Slackbladder, 21 February 2013 - 13:46.