On a 2.0 beta machine, I've been trying to run my wi card -- a Lucent 
card -- in promiscuous mode while tracking down some infected Windoze 
machines.  The network here at the IETF meeting is quite busy; possibly 
as a result, the card frequently drops and reaquires carrier.  (I have 
some patches by David Young that let me monitor that card via ifwatchd, 
so I see all of the transitions.)

Here's the card info:

Aug  1 11:39:43 berkshire /netbsd: wi0 at pcmcia0 function 0: Lucent Technologies, WaveLAN/IEEE, Version 01.01
Aug  1 11:39:43 berkshire /netbsd: wi0: 802.11 address 00:60:1d:f0:34:fb
Aug  1 11:39:43 berkshire /netbsd: wi0: using Lucent Technologies, WaveLAN/IEEE
Aug  1 11:39:43 berkshire /netbsd: wi0: Lucent Firmware: Station (6.16.1)
Aug  1 11:39:43 berkshire /netbsd: wi0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps

Here's a typical carrier glitch set:

Aug  2 22:46:04 berkshire ifd: wi0 interface-CarrierDown ( ) --------------------
Aug  2 22:46:05 berkshire ifd: wi0 interface-CarrierUp ( ) --------------------
Aug  2 22:46:28 berkshire ifd: wi0 interface-CarrierDown ( ) --------------------
Aug  2 22:46:29 berkshire ifd: wi0 interface-CarrierUp ( ) --------------------
Aug  2 22:46:52 berkshire ifd: wi0 interface-CarrierDown ( ) --------------------
Aug  2 22:46:53 berkshire ifd: wi0 interface-CarrierUp ( ) --------------------
Aug  2 22:46:54 berkshire ifd: wi0 interface-CarrierDown ( ) --------------------
Aug  2 22:46:55 berkshire ifd: wi0 interface-CarrierUp ( ) --------------------

Note the short duration of the outages; also note how frequently the 
glitch can occur.

For various reasons, I'm pretty certain the same thing happened on 
1.6.2 -- at the least, I do know that the card became almost useless 
when I had monitoring turned on.

		--Steve Bellovin, http://www.research.att.com/~smb