Well....we've got a treat for you. Here's a link to a video of PS2FTPd by Wank3rs in action on the PS2. In the video, they access the Memory Card Files as well as the HDD....although the partitions seem to be hidden folders.
The read speads are about 1k/sec whereas the write speeds are about 10k/sec.
You can get the video here
Use the latest MS codecs to view this.
Thanks to Loy for the headsup.