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.
Closing this one, since the file is selected on double-click, which IMO should be sufficient feedback on thunars side. Looks like that was not the case in 2006/2012.