There's currently no visual feedback when opening a file using double-click. If an application takes some time to show it's splash screen (or don't even have a splash screen and takes a long time to start) and this application doesn't support startup notification (or Thunar was compiled w/o sn support), then the user gets no feedback whether or not he/she really double-clicked the file. The suggested solution would be to add some kind of visual double-click feedback, maybe ala OS X Finder (cairo may help here).
Moving to 0.4.0rc1. We'll see...
Moving to 0.5.0rc2.
Moving to 1.0.0final.
Would be nice to see something like this happening.