Comment 8 for bug 1387199

For the record, I've a MacBook Pro 8,1 using broadcom 4331 chip. I find the bcmwl 6.30 driver consistently unreliable, packets just stop sending randomly and only solution is module unload & reload. I've had much more success (not perfect tho, but 99% reliable) with the older 6.20 driver.

I spent a little time forward porting 6.20 to vivid kernel (3.19). If you're curious, you can give it a go here:
http://people.canonical.com/~gerboland/bcmwl-kernel-source_6.20.155.1+bdcom-1ubuntu0_amd64.deb

I am back to my 99% reliable wifi as a result. If it helps you, do let me know!
-G

P.S. the package version is older than the vivid supplied one, so you'll need to pin (apt-mark hold) it to prevent it being upgraded.