Hmm. Can't get through to the HDD again. My data transfer still seems to be progressing though.
I really hope this only means the data cable is just getting old.
take2: Yeah, it seems like reading off it is painfully slow while writes are going through normally.
take3: Never mind, the write simply got stuck, almost freezing the machine as well. Once I stopped it, I can dig into the drive, but nothing really comes off it at a steady rate. I deleted a likely corrupt file, and now I can access things at decent speeds.