… I would buy Flickr. I would dedicate time and resources into making it a very good standalone photography sharing and storage platform. I would bring in users and focus groups and development experts, and more. Get feedback. Start building. Start improving. Keep it standalone.
… I would buy a minor league sports franchise, perhaps a USL or USSL team. Not only would I build the club as much as possible, keep the fan base engaged (it’s all about them) but, I think it would be fun doing this.