Want to see the loudness and peak information on the song(s) you're playing on Spotify?
I just discovered this fun little thing called "Spotify: Where is the Drama?" (http://static.echonest.com/WheresTheDrama/). Music Hack Day hall-of-famer Paul Lamere’s web app automatically finds the most dramatic part of any song on Spotify, and plays it for you with a single click. It works by analyzing the loudness profiles of the songs, to find the passage with the biggest build-up. To try it, simply click here while playing any song through Spotify. Don't ask me what the numbers mean though... it's a fun little visual graph for what it's worth!
And if you're working on a song and want to know how it will turn out in regards to loudness normalisation when played in streaming mediums who have loudness control on playback, then head on over to www.loudnesspenalty.com ... or as they say: "Find out if your music will be turned down by YouTube, Spotify, TIDAL, Pandora and Apple Sound Check. Discover your music's Loudness Penalty score, for free."
PS. Here's another interesting (YMMV) thing for analyzing Spotify platlists: http://sortyourmusic.playlistmachinery.com/