I'm a new Playbook user / fan, and noticed frequent dropping of wifi as well. I'm using a D-link DIR-825, and solved the problem completely by updating the firmware to the current version. (1.13) Hope this is helpful to some of you....
I get it too, its uaually when the PB goes into standby mode and i then have to turn off wifi and mobile networks and then turn em back on and all is ok, but at times i could be browsing a website and all of a sudden it won't load the next page and i have to turn off wifi and mobile network and turn on again.
I am not sure what the issue is but i think its to do with the PB sending a signal out and if your reading a webpage and so forth for too long or in standby mode it appears to the PB your not connected so it shuts the wifi internally off as if it was in a sleep mode.
Werid and annoying, but just turn on and off wifi and mobile networks and poof it be back working again np's after say a minute.
