Coming from iTunes I really liked the Smart Playlist feature so I created an app to create and push them to Spotify. It currently only uses Songs you've saved to "Your Music" but I plan to expand it to use other sources such as specific playlists.

Any feedback most welcome!

I like the idea! What you also could do to expand the smart playlist feature even more is if you give in an artist name, and only put in related artists' songs. The current features you have implemented are only based on search queries if I'm not mistaken.

Also the playlist scrobller you mentioned would be a great option. What about groups of playlists? What about playlists you follow?

One big plus is the era's playlists already at hand! I think it's a neat thing to have!

There is a really cool Spotify playlist builder here: http://smarterplaylists.playlistmachinery.com/index.html

And it's actively maintained by some guy on Twitter.