Just for the record my laptop (running F12 x86_64, and with an Atheros card) is presenting the same problem as MuadNu's. Restarting NetworkManager does not help either. The thing is that the machine didn't have problems before with F11 or with early F12, apparently it is down to some recent update (I am tempted to say "kernel update" because apparently both of our affected wifi cards's support is built in there).
I still have to try that command "modprobe" but meanwhile madhavdiwan, can you please elaborate a little bit on that "signal strength" or power thing? I remember having altered my router's default configuration raising the signal strength (but again the router is very far from the computer), is that related?
Notebook: Acer Aspire 5536-5112.
AMD Athlon X2 QL64 @ 2.1GHz, 4GB DDR2 PC2-5300, ATI Radeon HD3200 (256MB), 250GB Toshiba HDD, HL-DT-ST DVDRAM GT20N
Fedora 16 x86_64
Netbook: Acer Aspire One A150
Intel Atom N270 @ 1.6GHz, 1.5 GB DDR2 PC2-4200, Intel Graphics (8MB?), 160GB Seagate HDD
Fedora 15 i686