I've just done the following..... zipped 2 100MB files into 1 zip file, transfer the zip file to the phone,(mass storage mode) extract the zipped files from the phone . All in a few seconds and with no errors!
Tried this with 6 films in a zip file, total size was 4.1gb, copied via usb in mass mem mode, copied back and forth 3 times, zip file remains in tact, im only running the 700mhz kernel tho at the moment, will try later with the 750 and 800 mhz
Tested a 1.4GB zip file containing 2 700Mb movies. Copied it back and forth multiple times (PC <-> phone mmc<-> to PC) Transfer speeds (8.4Mb/sec write, 9.4Mb/sec read) : 16GB card No errors! (zip error test with winrar)