I use the 3-argument form of open when I don't intend the script to be usable on 5.5, which happens more and more often.

But I always make sure to quote the filename, because users give their files weird names that even can look like an error message. I always give the error message some more context, so I can later on grep the source program for the line where the error was raised:

  open F, "<", $file
    or die "Couldn't open '$file' : $!\n";
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Supposedly, there is only one place in the program where the message Couldn't open occurs of course. The idea of reversing the filename is interesting - that way, the interesting bits (filename and error message) are at the start and at the end of the "line" - using my way, the interesting bits clog together at the end.

I prefer my style, of course :).