Tested on NetBeansIDE-release35-200304062350-linux.bin
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My idea of polite and gentle installer's behaviour
when trying install it into non-empty directory is
that the installer should interact with a user in
this way:

1) user choose non-empty dir
  Installer should tell it the user: 
    "you select non-empty dir! Would you like
still continue
    installation into this dir?"

And this question has to come imediately or
maximum late possibility is when pressing NEXT button.

 There alsou could be more polite behaviour, like
detection other version of the IDE so, the
installer then should inform the user about it
(please see the issue #32524 where Richard
describs how the installer could behave when deal
with such situation)

But in this basic case, which I think will be till
now enough...
Should ask user already mentioned question...
And if user respons
YES
then it should continue in istallation, and when
the file conflict happens (file already exists in
the destination directory), Installer should ask
user about overwritting with folowing possible
answers:
"yes, yes to all, no,  no to all" and maybe cancel?


if user say
NO (for installing into non-empty dir)
then installer should stay in install dir's
choosing panel.