Are you using fileloggerdemo?
I got the fileloggerdemo working. I changed:
result = FileLogger::append("data.log", buffer, length);
to:
result = FileLogger::append("data.[glow]txt[/glow]", buffer, length);
On my PC, fileloggerdemo loads as a notepad text page; my PC is using Windows Vista. On the sd card, create a file named data, allow the notepad software to add .txt.
Filelogger woks ok, it adds data to the end of the sd file and does not over write previously recorded data. However, I just started working with it, and cannot get data on the card other than in ascii code unless data is added as text to the array called 'buffer'. There's a bit of confusion with that part.
Have you tried MMC/uFat2 and Deviceprint at this location (SD/MMC From the ground up)>(http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235125412) Problem with that system is that previously recorded data is overwritten if you stop and restart.