Answer: When your competitors start to gang up on you.

According to the New York Times this week, that time is now for Facebook, whose rivals have grouped together to take on the social networking phenomenon.

NYT reports that "an alliance of companies led by Google plans to begin introducing a common set of o standards to allow software developers to write programs for Google’s social network, Orkut, as well as others, including LinkedIn, hi5, Friendster, Plaxo and Ning."

The paper says the strategy is aimed at "one-upping Facebook", which has also opened its services to outside developers. Since then, more than 5,000 small programs have been built to run on Facebook site, some adopted by millions of Facebookers.

By being a holding pen for other programmes - from online scrabble games, to football score predictors and music appreciation clubs - Facebook is able to capture a lot of attention, from both users and programmers. And no doubt, advertisers.

A Google spokesperson confirmed the plan, saying it was aimed at getting programmers writing for applications other than Facebook.

“Facebook got the jump by announcing the Facebook platform and getting the traction they got. This is an open alternative to that.”

The move comes after Microsoft’s recent purchase of a stake in Facebook, and the new alliance includes business software makers Salesforce.com and Oracle.

Meantime, for Facebook users tired of being bitten by Vampires and compared to Hollywood stars, a new community website is targetting a large but mostly untapped market - older internet users. Saga Zone, created by the insurance and holiday company, has launched with the aim of becoming the social website of choice for the over-50s.

Users must be 50 and above, and members can create their own profile pages, contact friends or join in online discussions. The site already has over 13,000 users, and the company hopes this will increase dramatically.

"Older people aren't shy of using the Internet - they have a verve for life that applies online as well as offline," said a Saga spokesman. "Thirteen thousand is just a drop in the ocean - in theory the membership is practically limitless."

Media regulator Ofcom recently found that surfers over 50 account for nearly a third of all time spent online by British web users. Sites such as Friends Reunited have already proved popular among more mature surfers. So far the oldest user of Saga Zone is 87.