I have the same Broadcom card but I'm still struggling, even after creating the blacklist-bcma file. In fact it would be fair to say I am pulling what little hair I have out over this problem! If you would be so kind, could you confirm for me:
1) Do you also have a file in the same modprobe.d folder called 'blacklist-bcm43.conf'?
2) If so, does it look like this?
3) In Ubuntu Software Centre, if you type in 'Broadcom', what files do you have installed? Do you have just 'bcmwl-kernel-source' and 'b43-fwcutter'?
4) Are you running the 64bit version of Ubuntu?
I'm hoping the answers to this will help me sort this problem out once and for all. Thanks.