I am not quite sure but I think I spotted pieces of Qt in the Spotify client. That would explain a lot of its somewhat odd behavior on OSX (wrong focus states on some buttons, nothing serious) and its very consistent cross-platform looks.

In Germany, its only competitor uses an AIR app. Since Spotify is not available in Germany and thus a slight pain to use, I would really like to use an alternative. But AIR vs. Qt... the AIR app does not work on case sensitive file systems (solvable), it does not recognize the Mac media keys, it is sluggish and playback is nowhere near instantaneous. And you have to install AIR and suffer through regular AIR updates and the like. Oh, and audio quality is noticeably worse.

Well, if the competitor you're talking about is Grooveshark: AFAIK, their adobe air client is for the most part a legacy application. Grooveshark used to be all flash in the past, so they made the desktop app with AIR.

They seem to invest all their effort into the (very good) HTML(5) client and into mobile apps now.

I think he was talking about Simfy.

http://en.wikipedia.org/wiki/Simfy

It's fine.. If you use pulseaudio, if you hate pulseaudio's latency and have falled back to alsa then suddenly the volume control doesn't work.

Luckily the windows version works fine under Wine , even though it does nag about "unsupported platform"

I find when I try to share songs with friends via the linux client, my friends never have the songs in their inboxes. But when I send the same songs via the windows client, they show up with no problems.