I wonder about how you claim that many programmers tend to use [] for qw. I always thought that qw() is the canonical way to use them. Of course it depends on the contents, but if you take a look at e.g. perldoc -f use and the examples therein - of course left aside what others noted already.
Well, I'm one of the people that use [] for qw. I very seldomly use () as delimiters; parenthesis already have a couple of meanings, using them as delimiters as well doesn't contribute to code clearity in my book.
My favourite delimiters are:
Operator Pref. Other
Delim. Delims
q, qq, qx {} <> // !!
qw [] // {} <>
s, m, qr // {} <> !!
y, tr // [] {} <>