While they are still laptop speakers, the new MBP has a much better set than in my previous 2.16GHz Core 2 Cuo (bought in October 2006). There's not a lot of bass, but watching online videos is quite good.
I have the late 2008 15" MBP and it seems like there are 3 drivers..
There seems to be a driver for the lower sounds coming from the keyboard area slightly to the right...
I thought my speakers were initially unbalance as I heard the right side louder than the left side but then I hear deeper sound emanating from the keyboard area when i put on the heavy bass music..
In fact if you see the teardown here: http://www.ifixit.com/Guide/First-Look/Mac/MacBook-Pro-Unibody/Page-11#s3002
You see there is a subwoofer there... they even mention it.