Is there anything new with respect to this driver? I experience the same problem (practically unusable connection, deteriorating fast under load with up to 80% packet loss). I'm using an Apple iBook G4 with it's built-in wireless card and WPA.
dmesg says: bwi0 at pci1 dev 18 function 0 "Broadcom BCM4306" rev 0x03: irq 52, address 00:11:24:2b:db:88 ifconfig says: bwi0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 lladdr 00:11:24:2b:db:88 priority: 4 groups: wlan egress media: IEEE802.11 autoselect (OFDM36 mode 11g) status: active ieee80211: nwid Schroeder chan 13 bssid 00:11:24:0d:17:89 45dB wpapsk <not displayed> wpaprotos wpa1,wpa2 wpaakms psk wpaciphers tkip,ccmp wpagroupcipher tkip inet6 fe80::211:24ff:fe2b:db88%bwi0 prefixlen 64 scopeid 0x1 inet 10.0.1.5 netmask 0xffffff00 broadcast 255.255.255.255