I updated unsuccessfully my Bash to 3.2.48 by MacPorts.
It seems that I do not have it active, since I get
echo $BASH_VERSION
3.2.17(1)-release
I'm guessing it's installed but not being used as your login shell.
You can change the shell using dscl on the command line.
At the dscl prompt type the following:
list Local/Default/Users
read Local/Default/Users/
change Local/Default/Users/ UserShell /bin/bash /opt/local/bin/bash
I have another example of dscl use on my blog if it helps.