I'm not sure if this is common, or not, so here is my question: how sensitive is the Playbook to wireless routers.
I have (among others), a pair of MacBook Pros, plus a Playbook.
The Mac finds the network, and can work with it until the cows come home.
The Playbook is sitting right beside the Mac right now, and can't see/connect the guest network.
I can't see any way to diagnose the signal strength, but is this type of behaviour normal?

This is off the top of my head since I don't have a Playbook, but is it possible that the device uses a different band than what your router has? If your router is not dual band, the Playbook won't work.
This is just a guess, but I do know that newer devices use a different band than the single routers use.

i have this issue at work with my tmo hotspot. i get no network connection, but it does ready my hotspot.
but it works out of work. sorry though i dont have a fix for this. i think i am just not getting enough signal on my hotspot. but i assume your home network is working just fine with all your other devices.

This might help

KB27735-The BlackBerry PlayBook is unable to connect to a saved WiFi network 0 1942388481