IF you have a 25 station unit, you may not want to have 25 stations on it. It's my understanding that for each station, the refresh throws 100 songs. If you listen to a channel for longer than that 100 song period, on the next refresh, it will add songs to that channel to reduce the chance of repeats. Yes, it actually is smart and looks at your listening happens! By using less stations than the unit can hold, you are freeing up space for additional tunes.
I don't as of yet have a unit...I just listen online. But thanks for the advice for when I do get a unit...which will be the first thing I do should Sirius-XM go belly up. Even if sat. radio, which I listen to in my car mainly, DOES survive (which as of now seems to be less and less likely), it would still be nice to have a Slacker G2 thingie.