The latest Crutchfield Catalog contains details about the strongly-rumored Sirius Stiletto. There is over a half-page dedicated to discussing the details; here are the most important features:

-built-in antenna for live on the go listening
-wifi available for places you cannot get live reception but have a wifi hotspot
-100 hours of playback, likely based on a 2GB flash drive
-can support MP3 or WMA technology
-car dock with direct entry and other features
-two batteries, a regular, and a slightly larger with extended playback
-MSRP: $399
-Record programming in up to six hour blocks
-Works with Microsoft’s Play for Sure, which allows you to use subscription services such as Napster or Yahoo! Music
-New Boombox being released for it
-Antenna headphones are INCLUDED with the base kit

More information, another pic, and a place to comment here