Update: Citing unnamed sources, Ars Technica is reporting that the 802.11n adapter will retail for $100, which will drop the currently available 802.11g unit to $80. No official word from Microsoft yet, though.

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what will it be used for ?

I can only assume that it will do the same thing as other wireless networking devices, provide wireless networking. :)

Wow back to 100 bucks for Wi-Fi on The 360... makes me glad I wired my house for Ethernet instead, one time job and I haven't had to worry or invest since.

Please Please Please! Be WPA2 Capable! =)

WPA2? why bother unless your hiding some major data that people want to steel.
(If that's the case WHY are you using wireless!?)

Just use MAC filtering and don't broadcast your SSID and leave it open, then people (If they can even find it) logon to your network notice things don't work. So they figure its a bum-spot and move on.

Living in a well populated area just using mac filtering I've never had any issues people will try once and move on.

All the encryption dose is use more resources and slow stuff down.

Guest - Just use MAC filtering??? Whats the point of that .. ? Why not use WEP while your at it . MAC filtering is the easiest of them all to go straight through. ...just scan the network (even if SSID brodcast is off it will be found) You will also see the other machines connected through the router.(and the mac adresses of them.) .....change your mac adress to one that you found ... you are in ... Then you can attack the router it self and add another mac to the filtering if you want to surf without problems furter on. (2 identical mac addresses in the same network can yield interesting results) ...
an on the note "why bother unless your hiding some major data that people want to steel" Well all wireless is breakable. But you might want to at least keep pedofiles surfing of your IP. Thats a reason to atleast encrypt you network as safe as you can.
Its not always what data someone would want to steal...its what they can use your network for and the leave the blame onto you.

I think the prices for these xbox360 wireless adapter things ridiculous. Hell with a bit guide of the web and a linksys router you can make your own, and it only cost you $60, and you now have a spare router.

Currently have my xbox 360 linked up with ethernet over power adaptors. Works well.