I am using the latest gnuradio trunk and the ../gnuradio-examples/digital/benchmark.... I have disabled all the data loggins but the rx_receiver.dat from the
/usr/local/lib/python2.5/site-packages/gnuradio/blks2impl/dqpsk.py to reduce the computational requirements.
So once the costas locks, there is still some error which is causing the blur constellation. But I think that for an almost 40dB SNR signal ( http://img212.imageshack.us/img212/551/screenshot13.png ) we should get much better results.
I have also tried via air interface getting similar results. My question is whether this is normal for the mpsk gnuradio block receiver implementation or I am doing something wrong.