Following up on this thread --
I just yesterday came across this. I'd been trying to figure out what had happened to our printer's network response time for months -- unfortunately the firmware upgrade happened at the same time as a lot of other changes, including a few changes to settings, and so I never suspected the DIR-655 as the culprit (and when going back to factory default settings didn't fix the problem, I assumed it was Vista being stupid).
However, now that I've downgraded to the 1.11 firmware again, the printer responds as quickly over the network as it does on the machine it's directly plugged into. Prior to downgrading, it took several minutes to open up the print settings window, and several more to actually print the document. Nothing else was affected -- file sharing with the print server, for example, was lightning fast.
I was running the latest firmware prior to this; and I had tried going through every set of options in the router and changing them, to see if I had changed a setting that could affect the printer speed. None of the changes helped -- I'm still hoping that D-Link will fix this issue in their next release, but seeing now that they didn't address it between September 01st and the later release of 1.21 doesn't exactly fill me with confidence or optimism.