DateTime.strptime("2009/04/16 19:52:30", "%Y/%m/%d %H:%M:%S").to_time
The format uses the same syntax as what you pass in to strftime to print out a date. The page http://snippets.dzone.com/posts/show/2255 has a complete listing of all format types.
I'm a software developer that has been doing professional web application development with Ruby on Rails. These are my postings of various things that I've figured out and learned that I thought might be helpful for other RoR and web application developers.
DateTime.strptime("2009/04/16 19:52:30", "%Y/%m/%d %H:%M:%S").to_time