I wrote a small benchmark to test this on my machine. The code has been tested in MinGW gcc and g++ under Windows 7 and g++ under Ubuntu 11.04. Guess it has to be modified slightly to run in MSVC, didn't test this.
The code doesn't use any C++ specific features, so it can be compiled with both gcc and g++, although I didn't manage to compile it using gcc under Ubuntu (problems with timing routines). Every test writes 100 MiB of data to the disk and reads it afterwards, checking the data for integrity. The first two tests use (f)(get/put)c and single byte reads/writes, the last test uses fread/fwrite with a block size of 1 KiB. There are two compiler switches that change the behaviour: "LINUX" for Linux systems (timing routines use GetTickCount on Windows, gettimeofday if LINUX is set) and "USEINC" to enable inclusion of getcput.inc that Shelwien posted above. Two #define statements (BUFSIZE and LENGTH) can be used to adjust the fread/fwrite block size and the total amount of data.
 Windows 7 64-Bit, MinGW gcc/g++ 4.6.1, -O3 -s
 Windows 7 64-Bit, MinGW gcc/g++ 4.6.1, -O3 -s -DUSEINC
 Ubuntu 11.04 32-Bit, g++ 4.5.2-8ubuntu4, -O3 -s -DLINUX
 Ubuntu 11.04 32-Bit, g++ 4.5.2-8ubuntu4, -O3 -s -DLINUX -DUSEINC
   
fgetc/fputc 12900-13800 ms 12800-13500 ms 2900-3300 ms 2800-3200 ms
getc/putc 700-900 ms 800-1000 ms 2900-3700 ms 900-1000 ms
fread/fwrite 300-500 ms 300-500 ms 750-1100 ms 750-1100 ms
- fgetc/fputc is the worst thing you can use in MinGW (~7 MiB/s), simply replacing it with getc/putc is both safe and gives a huge speed boost (> 100 MiB/s)
- For the original gcc/g++, it seems there is no huge difference between fgetc/fputc and they are faster than MinGW's, although they are still quite slow (30 - 40 MB/s)
- The file getcputc.inc that Shelwien posted above doesn't do much for MinGW, but is perfect for the original gcc/g++
- Using fread/write or buffered I/O is the best choice, but depending on the task, might lead to some programming work.
- The observations match those from Matt, VC++ seems to act similar to gcc/g++ under Linux (no difference between fgetc/fputc and getc/putc, but boost from getcputc.inc)