Lately I've been having trouble keeping a connection to wifi, first at home and now at work.  What happens is that after a while I'll notice that my phone is using 3G.

If I go into my wifi settings, I'll see a strong signal from my router. When I try to connect manually,  I often get the message,  "Failed to connect to network" with no further details.  (There's a special place in hell for those who write error messages that give no indication of the nature of the problem.) Other times I can connect,  but the signal is reported as weak and drops quickly. 

My computers can connect with no problems and report strong wireless signals.  My roommates have no similar problems. 

I have a Galaxy Nexus running Jelly Bean.  My roommates have a Galaxy Note and a Galaxy S2, respectively,  both on ICS. 

What's wrong with my phone? 

#Additional details

* My phone is rooted but running the stock ROM.
* I first noticed this problem while using Tasker to [implement a Bluetooth wireless leash][1]. I've stopped using the leash--and Bluetooth entirely--but the problem persists. I'm still using Tasker for other things.
* In trying to track down this issue, I disabled "Avoid poor connections" but that change had no effect.

[1]: http://android.stackexchange.com/a/27485/14562