Performance-wise, you certainly won't get anywhere near the nominal 300Mbps with any draft-n router, but speeds slightly over 100Mbps are now possible in ideal conditions. With the D-Link we typically managed about 50-80Mbps in real-world testing with matching adapter cards. However, while we saw faster average speeds with the D-Link as compared to early MIMO routers like the Belkin Pre-N, the Pre-N still has slightly better range. The D-Link could not sustain a connection in the farthest room from our router, while the Belkin can, albeit slowly. Regular 802.11g clients can also connect to the D-Link, and will get much improved range and signal strength. This translates to faster performance, although still limited to 54Mbps. We tested using the mixed 802.11b/g/n mode, with auto 20/40MHz channel selection, which is what we expect most people will use. Performance will be maximized in the 802.11n-only mode, but that would lock out any legacy 802.11g clients, including visitors.
We had no problems with interoperability with several different draft-n and g adapters using the auto WPA/WPA2 encryption mode. When draft-n routers start getting Wi-Fi certified, you'll be assured of interoperability, but it's not too bad now. What we did have trouble with was the Wi-Fi Protected Setup feature, which is supposed to let you automate encrypted connections between devices and the router, but few adapters support it yet.
For a top-performing router with a great feature set and low price tag, it's hard to beat the DIR-655. If you have a need for the speed, both wired and wireless, we no longer see any need to sit on the draft-n fence.