I have an HP laptop with an integrated Broadcom controller:
02:00.0 Network controller: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller (rev 01)
I recently upgraded to Fedora 18, and have noticed a big difference between wireless networking performance. With Fedora 18 running, and sitting about 10 feet from a Linksys WAP54G access point I get "one bar" on the Gnome icon... if I double the distance, I start losing the connection.
If I reboot to Fedora 17, I get three/four bars at 10feet, etc.
I've checked the internal antenna cables, and made sure that each OS is running the most up to date kernels. I even used a spectrum analyzer to look for noise in the 2.4GHz spectrum. I don't have any external USB WiFi adapters to test with.