I've been using this reader/writer for a few months now and I've been using it exclusively as a reader up until today when I needed to write some files to do a firmware update. Well much to my frustration and disappointment, I discovered that this only works as a reader on my computer. Anytime I tried to write something to the card I would get a message saying that the drive was read only.
I tried two different SD cards, 3 different computers(1 Vista, 2 XP), and a registry hack to force the drive to write. None of this worked for me (I also have USB flash drives and hard drives and I can read and write to those just fine). Finally, I realized that all I needed to do to write files to the card was to load the SD card to my camera and to use a USB cable to connect it to my computer, this allowed me to write to the card. It did take me a while to figure out that it was the reader and not something else. For the record, yes I checked the manual "lock" button on the card and the card was not set to read only.
This is still useful to me as a reader so it still gets 3 stars because it works fine for that and I seldom need to write to files to a card but its still a disappointment.