Users noted that the speed of file creation decreased after migrating to Samba (linux FC15 x64,3.5.12-72.fc15). We use specific software  that creates files on Samba Share.
I made test software (run on win7, comiled with borland C5.5):
#include "stdio.h"
#include "stdlib.h"
#include "time.h"
void main(int argc, char *argv[])
{
int fsize=40000000;
int i=0;
FILE *to;
char str[]="0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890";
time_t start, end;
double diff;
time(&start);
to=fopen(argv[1], "w+");
for(i=0; i < fsize/100; i++)
    {
        fprintf(to, "\n%7d-%s",i, str);
    fflush(to);
    }
fclose(to);
time(&end);
diff=difftime(end,start);
printf("\n \t time_diff =  %.2lf", diff);
}

The result (in my enviroment):
test.exe \\windows_share\test.txt  - 2 seconds
test.exe \\linux_samba_share\test.txt  - more than 35 seconds.

The same time, copying large file to\from samba share gives more than 75 mbytes/sec (over gigabyte ethernet)