Flipboard, the popular news and feature aggregator for the iPad that turns content from blogs, websites, tweets and Facebook links into a magazine-style layout, has recently announced that it has added Harvard Business Review and GigaOm to its stable of content contributors. The two new acquisitions, announced today on the company's Twitter feed and blog, continue a string of recent additions that include architecture publication Dwell, photography site Fotopedia and news organization Al Jazeera (English).