echo 'export PATH="/opt/local/bin:$PATH"' >> ~/.profile

adds 'export PATH="/opt/local/bin:$PATH"' to the end of your
~/.profile which probably is where your shell setup info is stored.
try looking at ~/.profile -- the export PATH stuff should be at the
end of the file.
Adding it to ~/.profile adds /opt/local/bin to the path on login, and
the 'hash -r' should have reevaluated the ~/.profile and added the
changes.

If you just want to try it without all that, you could just do

export PATH="/opt/local/bin:$PATH"

which will add /opt/local/bin to the path.
then

ruby -v

should be 1.9 assuming the binary is in /opt/local/bin.

Nick