1. Download site like rapidshare and other crappy host. Inconvenient captcha and required paypal. Bitcoin can possibly take both roles and streamline the whole process. Suggested by Kiba.
That could be an interesting project. I'd be willing to work on the technical side but not sure I really have time to do proper support/marketing. Anyone interested in partnering up?
There will be nothing to market if there aren't anything to market. I suspect it required maybe only a week of development if you're competent. Other than that, it's about gaining critical mass of stuff to download before explosion, I suspect. Marketing can be something like gathering desirable and not illegal stuff to download, curating it, etc and than giving the link to people who want it. That can be done in your spare downtime until you find marketer worth his salt of set up an affiliate program that incentivized people to market for you.
Actually, I didn't suggested it originally, but somebody else did in the thread about p0rn.
( Those who are fans of IP enforcement should just skip this part. Just sayin'. )
That was me, and I was specifically talking about targeting the less than legal area of file sharing.
Put simply, you're just not going to find legal content that will be effective in that market. Anything like OSS is mirrored for free and people aren't going to pay to download. Content owners aren't game - it'd be just another CDN to them, why would they pay in bitcoin, and why would their users pay per download/MB/GB when they're already paying for the content? That niche is solely about pirated content - like it or not.
Marketing would take hardly any effort, as I'm sure (with a good enough user pay flow) we could offer higher conversion rates and payouts for affiliates than the other shady CC required websites. It would take time to work out a business plan, but the actual development would take no time at all. (I could do it in a couple of days with a full-time effort) The files themselves could be shoved onto S3 or something. Just have to have someone handy with numbers to make sure it's profitable - otherwise nobody's going to waste their time.
Something like x amount of BTC per GB or MB (instead of a monthly membership), with an affiliate system would take over that market. Lots of people are willing to pay for better access to niche pirated content, but are reluctant to offer up CC and personal info directly for obvious reasons.
I also don't see how bitcoin could be used as a captcha, those are used to make sure there's a human on the other end and not a spam bot...you could easily automate the payments. For this niche, it's paying for high bandwidth, concurrent downloads of pirated content; it just won't work otherwise IMO.
Agorist developers apply within.

2. Advertising clearing house like
http://projectwonderful.com. Suggested by mskwik.(I used projectwonderful to make tiny bit of money. I wonder if I can get more money from a bitcoin advertising clearing house)
We are working on a bitcoin business directory so an advertising clearance house would be a natural fit with this. There is one developer working on the directory at the moment so another drupal developer or two to help us out would get it done a lot quicker.
Moved #2 to niches being worked upon.
Ugh, Drupal. ::wilhelmscream:: I'd be willing to develop an advertising clearance house - I actually have a lot of industry experience there.