When the AP signal is very poor, b43 produces this sometimes (rarely):

wlan0: associate with 00:1a:2a:b8:75:21 (try 1)
wlan0: associate with 00:1a:2a:b8:75:21 (try 2)
wlan0: associate with 00:1a:2a:b8:75:21 (try 3)
wlan0: association with 00:1a:2a:b8:75:21 timed out
------------[ cut here ]------------
WARNING: at net/wireless/mlme.c:341 cfg80211_send_assoc_timeout+0xa8/0x140 [cfg80211]()
Hardware name: A6Tc
Modules linked in: usbhid hid usb_storage stkwebcam videodev v4l2_compat_ioctl32 ohci_hcd ehci_hcd usbcore nls_utf8 nls_cp866 vfat fat lm90 iptable_nat nf_nat xt_recent xt_tcpudp nf_conntrack_ipv4 nf_defrag_ipv4 xt_state iptable_filter ipt_addrtype xt_DSCP xt_dscp xt_string xt_owner xt_NFQUEUE xt_multiport xt_MARK xt_mark xt_iprange xt_hashlimit xt_conntrack xt_CONNMARK xt_connmark nf_conntrack ip_tables x_tables snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss vboxnetadp vboxnetflt vboxdrv nouveau arc4 ecb ttm cryptomgr drm_kms_helper crypto_hash aead pcompress crypto_blkcipher crypto_algapi drm b43 agpgart asus_laptop fb i2c_algo_bit snd_hda_codec_realtek mac80211 sdhci_pci cfbcopyarea sdhci psmouse evdev cfbimgblt rtc_cmos r8169 sr_mod mmc_core cfbfillrect sparse_keymap thermal snd_hda_intel cfg80211 rtc_core video snd_hda_codec mii snd_pcm backlight output sg led_class rtc_lib ac battery snd_timer snd snd_page_alloc ssb nls_base k8temp i2c_nforce2 hwmon button cdrom unix [last unloaded: usbcore]
Pid: 1305, comm: phy0 Not tainted 2.6.34-gentoo #5
Call Trace:
 [<ffffffff81037dc8>] warn_slowpath_common+0x78/0xb0
 [<ffffffff81037e0f>] warn_slowpath_null+0xf/0x20
 [<ffffffffa0142fe8>] cfg80211_send_assoc_timeout+0xa8/0x140 [cfg80211]
 [<ffffffffa0207c6f>] ieee80211_assoc_done+0xaf/0xc0 [mac80211]
 [<ffffffffa0209843>] ieee80211_work_work+0x4f3/0x11a0 [mac80211]
 [<ffffffff812afedd>] ? schedule+0x2dd/0x730
 [<ffffffffa0209350>] ? ieee80211_work_work+0x0/0x11a0 [mac80211]
 [<ffffffff8104ae7d>] worker_thread+0x16d/0x260
 [<ffffffff8104f450>] ? autoremove_wake_function+0x0/0x40
 [<ffffffff812b24f9>] ? _raw_spin_unlock_irqrestore+0x29/0x40
 [<ffffffff8104ad10>] ? worker_thread+0x0/0x260
 [<ffffffff8104efce>] kthread+0x8e/0xa0
 [<ffffffff81003114>] kernel_thread_helper+0x4/0x10
 [<ffffffff8104ef40>] ? kthread+0x0/0xa0
 [<ffffffff81003110>] ? kernel_thread_helper+0x0/0x10
---[ end trace ba6bf11a4e0cd829 ]---
wlan0: authenticate with 00:1a:2a:b8:75:21 (try 1)
wlan0: authenticated
wlan0: associate with 00:1a:2a:b8:75:21 (try 1)
wlan0: RX AssocResp from 00:1a:2a:b8:75:21 (capab=0x31 status=0 aid=28)
wlan0: associated

But anyway, the card can connect to AP after this crash and everything works fine. I don't know is it important but seem scary :)
It happens only with 2.6.34, previously I've never spotted something like that (also, I've started to use nouveau from 2.6.34 instead of proprietary nvidia).
The card is broadcom 4318.