No: it doesn't even seem to play back embedded in the page. It launches Spotify and then starts playing the selected track. If you don't have Spotify you're prompted to download it.
OK so it's basically the same as on Facebook then. Not very exciting...
You actually need a Facebook account to use Spotify. Not very exciting at all.
I use Spotify without a Facebook account. You have the option of logging in with your Facebook account, or creating a Spotify account.
It's no longer possible to create a Spotify account, you have to login using a Facebook account.
Now that's just messed up.
No. All the button appears to do is open spotify and play the requested song. It does at least sync that playback to the widget though so you can see the song progress and interact with it etc.
No, if you don't have Spotify it asks you to download Spotify and log in.