Commerzbank are enormous and have enormous exposure to Italy in particular. I wouldn't buy shares in them, buy I have no problem with depositing money with them. Shareholders are selling because they will probably have their holdings diluted by recapitalisation. Depositors should welcome recapitalisation.
Two things to remember - Germany is not broke, and like they already did in 2008, they can and IMO will recapitalise Commerzbank with public funds if necessary. Secondly - if they did let it go under, you have the German deposit guarantee scheme to fall back on. That is a world away from the Irish government promising they'll cover you.
Great widget here for seeing how different banks are stressed.
graphics.thomsonreuters.com/11/07/BV_STRSTST0711_VF.html