Frankly speaking, I couldn't understand most of dialogues. And, I also couldn't follow the story of movie. I think they didn't speak regular English. It's too hard to listen for me!
So, I'd like to write about three things what I felt and remembered.
At the beginning, three guys who are Everett, Peter, and Delmar break away from prisoner's work place for 'treasure'. It was very interesting to me. They just escape for the treasure - although they aren't sure it's real. Their behavior is so funny and thoughtless. I love a no-plan adventure story like that.
Secondly, three guys meet with sirens by chance. After being tempted by them, Everett and Delmar recognize Pete's disappearance and see only Pete's clothes. At this time, Delmar sees a toad that is jumping from inside of Pete's shirt. Delmar trusts that the toad is Pete! His silly action is so ridiculous.
And last, I still hum a song 'I am a man of constant sorrow'. It makes me to search on internet!. I like charming country music. And the singer's voice is quite good.
Even though I didn't know the whole story of 'O brother', I think it has a lot of fun and touching episodes. So.. I like it

Teacher's note: There is no need to understand every word of this beautiful story to appreciate it. Looks like you felt some appreciation. I hope you watch this movie again after you English gets better. Try these web sites.
http://www.youtube.com/watch?v=08e9k-c91E8http://en.wikipedia.org/wiki/Man_of_Constant_Sorrow