Trouble in Automator's Shell Script after OS X 10.9 Mavericks upgrade
I think you were close and that the following should work:

cat &gt;&gt; ~/Dropbox/ClipBoard/Appunti\ Mac\ del\ $ (date "+%Y-%m-%d").txt


You had smart quotes in your sample and that won't work and you left out the plus in the quoted format string which you had included in your original.