The math:
Napster To Go: $14.99 per month, download unlimited number of tracks unlimited number of times to an MP3 player. Cannot use the tracks anywhere else, cannot transfer them, cannot burn them to CD, cannot convert them without sound quality loss.
Napster Light: No monthly charge. Unlimited listening to 30 second music streams (browse). Purchase tracks for 99 cents each or albums starting at $9.95. You can ONLY burn purchased tracks to CD, you cannot burn or copy streaming music.
Napster (standard): $9.95 per month. Unlimited listening to music streams. Purchase tracks for 99 cents each or albums starting at $9.95. You can ONLY burn purchased tracks to CD, you cannot burn or copy streaming music.
You must have a current Napster account to listen to ANY music purchased or streamed from Napster.
Basically, the iTunes Music Store is most like Napster Light. The main difference is that you can't stream entire songs. Also, the music catalog is much larger on iTMS and there are audio books and other content. Plus, of course, Napster music won't play on iPod.
I suppose Napster To Go isn't bad if you don't care about keeping music permanently. You can download tracks to your MP3 player whenever you want and it never costs more than $14.95 per month.