Hi all
I'm testing my DIR-300 with 1.5.X (Built 20120114-2352 git@10d29bc) (pre - 1.5.3)
Everything appears to work fine
I must note the GUI is sluggish but I suspect this is the way with new firmware on old machines?
I should also note that after flashing your device you should leave it powered up for a long time (don't know the exact time) to finish configuring.
I'm going to suggest 30 minutes on the safe side.
I was having problems until I plugged in my serial cable and could see that the device had not finished installing.