While I'm neck-deep in timezone land, I'll also address one little problem wih the tztime plugin. While running the functional tests I began getting errors like the following:
NoMethodError: undefined method `tzinfo' for #<TZInfo::LinkedTimezone: UTC>
I could fix it by forcing a timezone into the TzInfo object at the beginning of each failing test - but that seemed a bit of a hack. Looks like the problem has been submitted as a bug in rails ticket 11150. The suggested codefix seems to work just fine, but requires more hacking on your vendor/plugins/tztime directory. Still, it's a one-line fix, so not much to do.
The failing tests were replaced with a new error:
<Tue Apr 01 00:00:00 +0000 2008> expected but was <2008-04-01 00:00:00 UTC>.
The failing line is in the functional test thus:
assert_equal Time.now.at_beginning_of_month, assigns(:month)
This is an instance of a problem I've seen before... ie that you don't seem to be able to compare Times with DateTimes, Dates or (now) TzTimes. The quick solution is to forcibly cast all your time-like objects into a common time-like object before testing for equality. My suggestion is to_datetime, which works for all the instances I've needed, thus the previous test case would become:
assert_equal Time.now.at_beginning_of_month.to_datetime, assigns(:month).to_datetime