I was having problems with weakening signal and dropped connections with my DLINK DIR 655 N router. I changed the settings in my router setup so it only broadcasts in b/g mode (since I couldn't rename the SSID's as Apple suggested).
This seemed to fix my problem and my connection has been full bars and no loss in connection.
This won't help if you are in a public place and defeats the purpose of N mode routers. It prob will work to set mode to N mode only if all your devices use N mode but I have some that can only connect to g mode.
I hope this makes sense and helps someone out.