time_zone_select() Trouble

I am having a lot of trouble getting my time zone select to default to the user's previously selected time zone. Here's my code:

<%= time_zone_select :other, :time_zone,   TimeZone.us_zones,   :selected => cookies[:time_zone] %>

This didn't work, so I checked all my cookie action (which seems fine) and finally tried the following just to see if it was working at all:

<%= time_zone_select :other, :time_zone,   TimeZone.us_zones,   :selected => "Hawaii" %>

That doesn't work either. Any ideas?

Here's what the API says about it: