Which XM Weather package are you subscribing to?

Does the subscription include the audio offerings, or is that
additional? How much?

I've got the Aviator package; it's $50/mo. Aviator Lite is $30/mo.
Music is
extra.

http://www.wxworx.com/aviation/service_pricing.php

Yeah, I want to know too. I'm drooling over this thing but I'm trying
to get a grip on the total cost. I'm also wondering if many rental
aircraft will have a place to tap in for power? Since I'm not a
smoker, I've never paid attention to the presence or absence of
cigarette lighters in aircraft.

Final question: if they do have outlets, what voltage? The Garmin is
12V but I think most GA aircraft are 28V.

The adaptor works on either one.

It's a lot of money at stake. I don't want to bite the bullet and
then find out it's not really that great because you can't effectively
power the thing in a rental C-172 or Cherokee.

Not a problem.