On Feb. 29, some people found a bit of spam in their email and one after another from around the globe hit "Reply All", demanding to be removed from the list. Unbeknownst to them, they had been signed up to a listserv so that each demand was being sent to all the people in the original email. Then, something strange happened. Camaraderie broke out.

Moving to "honour and standardise the attribution of discovery" on the web, Brainpickings.org's Maria Popova proposes curators attribute their sources one of two ways, using the "Curator's Code". A "via" indicates direct discovery, and would be used for reposting a bit of content with little or no change. A "hat tip" would signify an indirect link of discovery, wherein content is just a jumping-of point for new material. Details are at curatorscode.org.

Youku Inc. is set to buy Tudou Holdings Ltd., in a stock-for-stock transaction that will make them dominant, with more than a third of the online video advertising market. Under the terms of the agreement, Youku shareholders and ADS holders will own approximately 71.5% of a newly combined entity, Youku Tudou Inc., and Tudou shareholders and ADS holders will own 28.5%. Together, the companies would control more than a third of China's online video advertising market.

After trialling content recommendation engine Outbrain on London24.com, the regional publisher reports an uplift in page views per visitor. The tools helps users find relevant content more easily and highlights sponsored recommendations on other sites, which the publisher gets paid for if clicked on.

Three years after it launched at the South by Southwest conference in Texas, which ends today, the location-based social network is gone. The moble phone app, which reported 600,000 users a year ago, also launched the same day as Foursquare, which has enjoyed a much higher level of popularity. Facebook hired Gowalla's founders and some staff to help build up its own location offering.

Fifty Shades of Grey by former British TV exec EL James was discovered on a web site, where it had attracted many readers, and marketed as an e-book. It later had a limited online print run. Now, thanks to social media, the racy romance novel has topped the New York Times bestseller list and a seven-figure paperback contract from Vintage Books is in the works.

Hoping to forestall copycat developers, Wrapp, the Swedish social gifting application, is expanding into other markets and on Monday it launched in the UK. It allows users to send free or paid-for gift cards through Facebook. The gift card industry in the UK is worth more than GBP4.5bn. Already, Germany's Samwer brothers are trying to copy the business model.

Despite the fact the Office of Fair Trading is probing Groupon in the UK, the national and regional newspaper publisher is going up against the likes of the daily deals service with one of its own, called Happli, this week. The publisher will be offering deals at both local and national level to bolster its connection with local businesses through its regional newspaper titles. It will face intense competition not only from Groupon and LivingSocial but from brands like BP and Time Out, which have entered the arena.

A new eye tracker that is smaller and cheaper than the company's previous model was unveiled by Tobii at last week's CeBIT show in Germany. It can track anyone's eyes in various environments, a key challenge for widespread use. The Swedish marketer envisions the IS-2 Eye Tracker's use in computer monitors, arcade games and slot machines and public infotainment systems. Two infrared projectors are used to illuminate a person's pupils, and then two small cameras register the positions of the pupils as they move.

Just in time for spring break, Sincerely's Postagram has launched its service in Europe, allowing users to send physical postcards made on smartphones to addresses here. It is expected to take off, especially in Western Europe in countries like the UK, France and Germany, which have strong traditions of sending greetings cards by post. The company says that 25% of its web traffic is non-U.S. The price for sending a card to any non-U.S. address will be $1.99.