Since Spotify arrived on the digital music scene last October, people have been flabbergasted by how fast it works. How could it possibly be able to search and index millions of files and then deliver you the music stream quicker than searching your own MP3 collection? The answer is three-fold. A peer-to-peer infrastructure, fantastic coding, and a massive cache.
The cache is the most interesting bit. By default, the program uses up to 10% of your hard drive for storing the music that it downloads. You can have a poke around in it by going to C:\Users\USERNAME\AppData\Local\Spotify\Storage on Vista, or the equivalent directory for other operating systems.
The files residing within are the music that plays when you double-click a track name in the software. Stuff you play gets saved to this directory, so that when you play it in the future, there's a local copy and it can find it faster. So can you pull out the tracks in a usable form to copy to your MP3 player?
The short answer is yes. The slightly longer answer is yes, with a lot of difficulty and if you don't mind breaking the law. For most people, it'll be beyond them - you'll need to use source code provided by dodgy open-source client Despotify, and you'll need to have a Premium account - because Despotify doesn't work with free ones.
In reality, it's not worth the bother. You'll eventually end up with a 160kbps OGG file. That's fine for streaming but when you convert it to MP3 to put on your MP3 player you'll lose even more quality. Even if you're not an audiophile you'll be able to hear the difference.
Simply put, if you're intent on breaking the law then in reality it's much easier to go to The Pirate Bay and get the tracks you want there. But why bother? As actually-quite-useful piss-take website Spotibay illustates, if people have fast access to music in a user-friendly way, then they won't bother with piracy.
Where that argument falls down is mobile access - even though Spotify's rolling out the mobile clients, what happens when you go out of coverage, on the tube or in rural areas?Then you're screwed, right? Well, if hints on the company's support forum are followed-through, then maybe not.
A post on the support forum requesting that the company provide cache-only playback for offline conditions met with a surprisingly positive response with the company, stating:
"An offline play mode is a feature we're looking at implementing at some point in the future. I think any feature we develop would likely have the option for the user to decide what is available for offline play."
If that functionality is extended to mobile, and there seems no reason to believe that it wouldn't be, then that could have massive positive implications for mobile clients - pick the albums that you want while in a Wi-Fi area and then while on the tube or even when you just have a 3G connection you can still enjoy music, as well as streaming when available.