Poor usability is the main reason behind the limited adoption of Google's services such as Gmail and Google Talk, according to Jeff Bonforte, senior director of real-time communications at Yahoo.

"[Google] definitely is lacking in usability," Bonforte said in a meeting with reporters at Yahoo's corporate headquarters.

"They don't have this intimate connection in usability with consumers that Yahoo has had for 10 years. When it comes to consumer applications, no-one is more successful than Yahoo hands down.

"And it happens over and over and over again. In every application, we are number one or two."

December market share data from comScore puts the number of worldwide Gmail users at 60 million. Yahoo is the world's largest web mail provider with 249 million users.

A similar picture is shown in the instant messaging market, where last May Google Talk accounted for 3.4 million users. Yahoo's 77.9 million users makes the company trail behind only MSN Messenger with 181 million users.

Google is receiving a lot of attention from technical users, but its search engine and online maps services are the only examples where the company has been successful in appealing to a wide audience, Bonforte argued.

"Usability to consumers at the mass level is the most difficult problem to solve on the internet," he said.

"There is lots of stuff that we can put out there for dorks and geeks like me, because we eat it up. But actually getting to something that is usable is extremely complex."

Bonforte joined Yahoo 18 months ago and heads up the company's messenger product. He turned down a position at Google at the time, he said, because the company is ruled by engineers and refuses to pay attention to usability.

Online application providers should focus on limiting the number of features they deliver, he argued. Where adding features will alienate users, Yahoo found that removing them can increase the time that users spend using the application.

"On [Yahoo Messenger for the] Mac client, I reduced the functionality by 30 per cent and increased usage by 35 per cent. As we take out features, it tends to do better with the mainstream users," said Bonforte.

Yahoo Messenger, for instance, offers a tool that allows users to share photos and provides a platform to highlight and discuss features within the images.

But the vast majority of users send the physical file instead of using the photo tool, causing 85 per cent of all file transfers on the client to be images.