I first read about the Air Magnet Spectrum XT on a blog post written by Marcus Burton http://www.cwnp.com/index/cwnp_wifi_blog/5203 and determined to try out this new product. After having used the Cognio product which is now owned by Cisco and also the much cheaper Wi-Spy product I determined to find out if I could use this product for troubleshooting and surveying that I do as a normal part of my job.
Soon enough I had the opportunity to test it out when a client I was working at began to have connectivity problems that I couldn't easily attribute to misconfigured AP's (I know they were configured right, because it was me who configured them!). I must say the Spectrum XT passed this with flying colors. My Wi-Spy adapter told me there was a problem somewhere but didn't really break it down. I didn't have the Cognio to compare it to with me, but the information that the XT gave me was comparable to what I had observed on previous troubleshooting engagements with the Cognio. It turned out the troublesome device was a projector with a wireless card of some sort in it. This took quite a bit of detective work to find as this device would go into a cycle of blasting out noise across the entire 2.4 spectrum and then quiet down just when we went searching for it. It seemed to me to be acting very like a FHSS device.
All in all I would highly recommend the XT to any wireless professional, its price point is reasonable for the functionality it gives and it is invaluable in troubleshooting and site survey work. One proviso with it is that in order to be able to see normal 802.11 networks you have to have an Air Magnet compatible wireless card to pick them up as the XT is just scanning for all the non-802.11 specific signals.
By the way, AirMagnet's Spectrum XT product works best with a Wi-Fi card from their supported cards list. But, it does work with any Wi-Fi card supported by Windows. Just not to the same level of detail.