DIWA Labs has tested heavyweight Panasonic Leica D Summilux 25mm f/1.4 lens that is one of few lenses for the Four Thirds format that can sport F/1.4. They tested the lens on the top DSLR camera from Olympus, the E-3.
DIWA Labs has also compared the Panasonic Leica D Summilux 25mm f/1.4 lens with its cheaper cousin from Olympus, the Zuiko 25mm f/2.8 pancake lens and it seems that the Leica is only marginally better than the Zuiko lens.
Read the full tests of the Panasonic Leica D Summilux 25mm f/1.4 lens here.
The tests done by DIWA Labs are very technical so you need to read their test guide to understand the test results.