In Ruby on Rails, what’s the difference between DateTime, Timestamp, Time and Date?

In my experience, getting dates/times right when programming is always fraught with danger and difficulity.

Ruby and Rails have always eluded me on this one, if only due to the overwhelming number of options; I never have any idea which I should pick.

When I’m using Rails and looking at ActiveRecord datatypes I can find the following

:datetime, :timestamp, :time, and :date

and have no idea what the differences are or where the gotchas lurk.

What’s the difference? What do you use them for?

(P.S. I’m using Rails3)