I'm reopening as requested by Andy, since this is happening to me with the latest Karmic kernels. rmmod iwlagn and then modprobeing it doesn't seem to solve the problem. Neither does suspend and resume or hibernate and resume. The only way I've found to get my wireless back after it happens is to reboot.

Linux hup 2.6.31-14-generic #48-Ubuntu SMP Fri Oct 16 14:05:01 UTC 2009 x86_64 GNU/Linux
HP 8530w

I get the same thing in the logs as everyone else:

Oct 28 11:55:56 hup kernel: [16878.980450] iwlagn 0000:03:00.0: Error sending REPLY_SCAN_CMD: time out after 500ms.
Oct 28 11:56:01 hup kernel: [16884.480124] wlan1: no probe response from AP 00:1f:33:cf:2e:4a - disassociating
Oct 28 11:56:02 hup kernel: [16885.080108] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:02 hup kernel: [16885.080121] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:03 hup kernel: [16885.581328] iwlagn 0000:03:00.0: Error sending REPLY_SCAN_CMD: time out after 500ms.
Oct 28 11:56:03 hup kernel: [16886.084966] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:03 hup kernel: [16886.084978] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:04 hup kernel: [16886.581343] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:04 hup kernel: [16886.581349] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:08 hup kernel: [16891.080241] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:08 hup kernel: [16891.080252] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:09 hup kernel: [16891.581523] iwlagn 0000:03:00.0: Error sending REPLY_SCAN_CMD: time out after 500ms.
Oct 28 11:56:09 hup kernel: [16892.081530] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:09 hup kernel: [16892.081541] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:10 hup kernel: [16892.581563] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:10 hup kernel: [16892.581575] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:14 hup kernel: [16897.080076] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:14 hup kernel: [16897.080087] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:15 hup kernel: [16897.581536] iwlagn 0000:03:00.0: Error sending REPLY_SCAN_CMD: time out after 500ms.
Oct 28 11:56:15 hup kernel: [16898.081297] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.
Oct 28 11:56:15 hup kernel: [16898.081308] iwlagn 0000:03:00.0: Error setting new RXON (-110)
Oct 28 11:56:16 hup kernel: [16898.581345] iwlagn 0000:03:00.0: Error sending REPLY_RXON: time out after 500ms.

(And it just goes on)

When I disable networking, remove and then modprobe the iwlagn driber and start it again, I get messages like:
Oct 28 12:07:56 hup kernel: [17599.534235] iwlagn 0000:03:00.0: PCI INT A disabled
Oct 28 12:08:06 hup kernel: [17609.176992] iwlagn: Intel(R) Wireless WiFi Link AGN driver for Linux, 1.3.27k
Oct 28 12:08:06 hup kernel: [17609.176995] iwlagn: Copyright(c) 2003-2009 Intel Corporation
Oct 28 12:08:06 hup kernel: [17609.178406] iwlagn 0000:03:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17
Oct 28 12:08:06 hup kernel: [17609.178417] iwlagn 0000:03:00.0: setting latency timer to 64
Oct 28 12:08:06 hup kernel: [17609.178469] iwlagn 0000:03:00.0: Detected Intel Wireless WiFi Link 5300AGN REV=0x24
Oct 28 12:08:06 hup kernel: [17609.219842] iwlagn 0000:03:00.0: Tunable channels: 13 802.11bg, 24 802.11a channels
Oct 28 12:08:06 hup kernel: [17609.219925] iwlagn 0000:03:00.0: irq 31 for MSI/MSI-X
Oct 28 12:08:06 hup kernel: [17609.223986] phy1: Selected rate control algorithm 'iwl-agn-rs'
Oct 28 12:08:06 hup kernel: [17609.236085] udev: renamed network interface wlan0 to wlan1
Oct 28 12:08:11 hup kernel: [17613.670604] e1000e 0000:00:19.0: irq 30 for MSI/MSI-X
Oct 28 12:08:11 hup kernel: [17613.730161] e1000e 0000:00:19.0: irq 30 for MSI/MSI-X
Oct 28 12:08:11 hup kernel: [17613.732385] ADDRCONF(NETDEV_UP): eth1: link is not ready
Oct 28 12:08:11 hup kernel: [17613.733761] iwlagn 0000:03:00.0: firmware: requesting iwlwifi-5000-2.ucode
Oct 28 12:08:11 hup kernel: [17613.743972] iwlagn 0000:03:00.0: loaded firmware version 8.24.2.12
Oct 28 12:08:11 hup kernel: [17613.935806] Registered led device: iwl-phy1::radio
Oct 28 12:08:11 hup kernel: [17613.935853] Registered led device: iwl-phy1::assoc
Oct 28 12:08:11 hup kernel: [17613.935895] Registered led device: iwl-phy1::RX
Oct 28 12:08:11 hup kernel: [17613.935944] Registered led device: iwl-phy1::TX
Oct 28 12:08:11 hup kernel: [17613.971988] ADDRCONF(NETDEV_UP): wlan1: link is not ready

And the link never becomes ready.