Ever since Slacker Radio decided to flee the hardware business, we've been looking forward to bigger and better things from its mobile apps. If the hands-on that Dave Zatz got with the version 2.0 software for iPhone is any indication we won't be waiting in vain, either. The big news here is station caching: that's right, users will soon be able to store music for off-line access, whether you're listening on a plane or in a dead zone. Exactly how many stations (and for how long) you can store is currently a mystery, although the reviewer said it took about 20 minutes to cache six stations, wi
