I'm a mac user also.
My DIR-655 works great, for raw speed, and windows machines seem to have no problems with it anymore.
However, any of my linux/mac boxes that use multicast to talk to each other using mdns (including my printers) have intermittent complete and total lookup failure for no reason I can coherently track down. Other than to determine that the DIR-655 itself is the problem (by swapping its predecessor back into the network as the gateway).
I do like the speed, but going along all fast is great, until one machine on the network experiences the mdns lookup failure that then seems to spread like cancer to all the others. Then they all fail to be able to lookup .local domains for an hour or so. Very frustrating.
I don't actually use USB, wireless or securespot at all, just the wired switch and WAN port.