This is a post from forever ago, but it is the first one that I have found that mentions my problem. I'm afraid I don't have any illumination on abfab's first stated problem (although hopefully he has solved it by now), but I have seen that the web interface, and in fact EVERYTHING that the drive does while there is an external USB drive is a lot slower.
I have a 750GB USB MyBook, and as soon as I connect it to my 1TB (single drive) MBW, all requests to the MBW become slower. The web interface takes 10-20 seconds to process requests (though they do seem to work). Opening the windows share of the disk takes forever. Opening the external disk also takes forever. It takes a good 60 seconds for windows to finish populating the files listing of the external disk (many folders, but not tons of files in any given folder). Once you get something playing, it seems to stream properly (TV shows, for instance), but any sort of back-and-forth interaction is terribly slow.
Even just copying files from one to the other or from my PC to the MBW drive takes 30 seconds to start. All the while, the MBW is doing the circle blink a lot, but seems to go black and then start blinking again, and I hear a good amount of drive clicking (not a click of death, just normal sounds) but they seem more intermittent than I would expect.
When I disconnect the external drive, I get snappy interaction with the MBW, copies to it go around 4MB/s (as expected) and the web interface is fine. The LEDs do the circle pattern with no pause as the copies are going. Is this a problem with just a few? Should I go through the reformat routine that fixes other peoples' corruption problem? I am currently copying about 250GB of files to the drive, and I'm 75% through. There has been no problem or glitch so far, so I don't have any other apparent problem. No hacking so far, just upgraded to the 2.00.18 firmware.