Just picked up a DIR-615. Excellent performance in AP mode, horrible in Client. The wireless connection is stable, 2-5ms ping times for 24 hours straight and no drops, but sits at 1mbit/sec in client mode. I currently have a small network of computers bridged wirelessly using this device.
Interestingly enough, I'm also handling a separate AP network with this router... so one AP mode network and one client mode at the same time. I am able to connect at full 54mb/s in G mode(over 1mbyte/sec transfers) on the AP side, but the client side only connects at 1mbit/s(70-90kbyte/sec transfers). This confuses me, because all other devices I've worked with virtual interfaces on limit both connections to the same datarate...
As a sidenote, the LUCI web interface is REALLY snappy compared to my wrt54gs v1 and asus wl500gp...I'm guessing that's the result of MIPS vs ARM...plus the extra 200mhz of clock cycles to make use of.
Also, thank you RoundSparrow for your builds, I'm currently using your march 8th dir-615 binaries. Saved me the time of reconfiguring my build machine =P