Running tests on Samsung Galaxy S II, using J Disk Benchmark 3.0 app (50MB size test data, 4KB buffer size):
Write: 20.4MB/s, 19.70MB/s, 21.8MB/s
Read: 21.3MB/s, 21.86MB/s, 22.13MB/s
Real life performance, however is different - when I use a USB cable and try to copy large movie from my PC to the phone, initially I get stable 20-23MB/s write speed, but after copying the first 500MB of the movie then the speed drops to 3-5MB/s and keeps coping like that to the end of file (1.7GB). That is a bit frustrating and I don't know what the reason is, but in general this memory works extremely fast on the phone.