Congrats one two milestones: launching and having paid users. I think I first saw FileSlap on reddit - well done.

I like the simplicity of the audio player. I can't pinpoint a niche off the top of my head, but I can see the appeal of sending a quick link, "Hey, listen to this". I know a few musicians who might be interested in using FileSlap for that purpose.

While I'm here, may I offer a suggestion for your website? I would keep that slider for view demo/see examples visible by default. I just read that I can view files without downloading them...my next question is how, say, PDFs are going to look on your site. I actually missed your "see some examples" link the first time I scanned the page. (You could then remove the "View demo" button and have a bigger call to action, but I'll leave the details to you)