Non UTC database with TimeZone support? (Rails 2.3.4)

I have an existing database where all dates/times are in PST and I'm
interested in adding time zone support for our users.

My setup:

# environment.rb
config.active_record.default_timezone = :local
config.time_zone = 'Pacific Time (US & Canada)'

With a before_filter to set each user's time zone.

All the documentation I've founds says your database needs to be in
UTC for this to work, but this seems to be working fine, including
adjusting times for daylight savings time. Am I missing something?
Will it implode during certain dates/times?