Dave from Google posted in two Google Maps Help threads that the public transit layer is not working on Google Maps.
There are several reports that it hasn't been properly working in any of the cities for the past few days.
Dave from Google replies yesterday saying:
Yes we're still working on a fix. We generally avoid giving ETAs on a fix like this because software can be a complex business, and things sometimes take longer than expected. The main thing we want to avoid is breaking something else while fixing this issue! Apologies for the inconvenience.
So, I am not sure when it will be resolved but Google is aware of the issue and they apologize.

Comments:
Moejontoya
06/28/2011 12:14 am
Its not working again right now.. 6/27/11
jarrett
04/23/2012 07:13 pm
And now! Apr. 23, 2012
Will I am
06/11/2012 10:40 pm
Not working here in san antonio
Toks
06/13/2012 09:37 pm
not working!
stan
06/19/2012 09:56 am
not working 19 june 2012
DJ ALLSTARRR
07/12/2012 07:19 pm
July 7 12'