There are plenty of threads in the Olympus forum the most recent two posts are about the XZ-1.
Mine is also a pocket backup camera, and it performs quite well.
Far better in low light that the E-P1, and the GH-1 that are in the travel camera bag.
I haven't compared it to the 1DmkIIN and 1DSmkII yet, but in low light I expect it to be comparable for noise - better despite the small sensor.