I'm using a D-Link DWL-G122 in versions C1 (and own a version B1, a D-Link DWL-122, a Linksys@Home 54g USB, and a Belkin F5D6050 USB -- insert sarcasm here), and have worked with (too) many similar Ralink or Prism-based USB wi-fi adapters on OS X over the last four years or so. One issue I experienced (with all of these adapters) was when the adapter was either under heavy load, or (especially) when using Internet Sharing in OS X, the adapter would randomly disconnect from its wireless network and lose all communication with the driver/config software. To fix things, it would require an unplug/replug to resume operation. With many people reporting this on the net, and having tried every suggestion I could find, I have finally found the answer that has since worked solid for over three weeks (and over 150gb of transfer) now without a single disconnection with any of my adapters!
Just for good measure, I tried (and failed) with these solutions:
A wide selection of Ma...