Have you seen it recently? I was very happy with it the last few flights/road trips I've used it on. A year ago it was awful--crashing all the time--but now it feels quite polished.
It's OK. It drains battery like mad and doesn't stream worth crap (I get maybe one song in five to play). But other than the battery issue, offline mode works reasonably well.
My theory about the battery usage is that Spotify uses Vorbis for encoding their files, and iDevices lack a hardware decoder for that.
It's pretty good, but it's astonishing to me that it still lacks type-ahead