Wired:Xiaoxin's cafe is full of Chinese students tapping away on laptops connected to the complimentary Wi-Fi. It's one of the few places here in Beijing where you can get away from the endless promotion of next year's Olympics. There are some parts of China's net life, though, that you cannot get away from, writes Danny O'Brien.

Next to me, a colleague is spelling out a problem with Google for the benefit of a friend.

Every time he types a particular term into the search engine, it's blocked by the infamous "Great Firewall of China", the government-run censorship system. The frustrating thing is that the word triggering the blocking is "zhen", a syllable used in any number of Chinese compound words. Ironically, one of the meanings of "zhen" is "to suppress".

By all accounts, I'm something of a free speech die-hard, but even so I was surprised by how much of an impediment to using the net the Great Firewall is within China.

British, Irish and US sites were regularly inaccessible in a way that was clearly a result of blocking rather than just poor connectivity.

Working in English online in Beijing means doing without Wikipedia or Livejournal. Random pictures disappear from Flickr; if you type one of the really hot terms, such as Falun Gong, you can expect your connection to be flaky for minutes afterwards.

It's also inconsistently applied to companies. The "Zhen" block only affects Google and affects both the US site and the specially censored internal Google.cn.

Yahoo and the homegrown Baidu.com suffer no such filters. Foreign companies admit that they are often confused as to the reasons behind blocks or what they are expected to do to conform with the dozens of Chinese legal authorities.

Domestic dotcoms are more circumspect, but it's clear that both they and the government are content to be more aggressive than is required by the letter of the law, both in blocking and preventing their users from posting "unsuitable" content.

Privately, some US experts suspect that Chinese net companies may even be involved in censoring their foreign competitors, using their influence to perform the "patriotic duty" of helping the firewall at the same time as hindering their commercial competition.

That said, for most Chinese net users, the firewall is a nuisance more than a hot topic of political complaint. In this developing country, most net use is still for business, not entertainment or education.

Bloggers and offline news gatherers are targeted by the firewall, but commercial transactions are generally safe.

Nonetheless, the unbalanced nature of China's censorship has already affected business ties between it and its rival on the world stage, the United States.

Last week, the US formally requested that the World Trade Organisation (WTO) establish a dispute settlement panel over China's regulation of films, books, newspapers, magazines and CDs, claiming that the censorship rules constituted an illegal restriction of free trade between the countries. Such a challenge is a short step from what Silicon Valley companies have been lobbying for: a similar complaint about the unfair effect of the firewall on US internet companies.

It's hard to tell whether it's the firewall or the long distances and narrow bandwidth between the Chinese mainland and US servers, but domestic websites definitely feel more spritely and less prone to random failures than their foreign source equivalents.

More seriously for China in the short term is the effect of the firewall on its image in the forthcoming Olympic year.

Billions of yen have been spent dusting down Beijing, paving city alleyways and placing a gleaming face to what the ruling party hopes will be China's debut as a mature new power on the world stage.

However, all the clean sweeps of the city will not help China's image if those millions of visiting athletes, dignitaries, tourists and reporters fall foul of the barbed-wire fences between them and the outside world.

Can Beijing bring down the wall? Perhaps the best result of the Olympics will be a temporary halt to the thousands of software filters and hand-edited blacklists that make up China's national censorware.

China's businesses and new middle class have never known a net without a firewall and its capriciousness may have led them to assume the net was always like this: with random drop-outs, delays and broken connections. Given a few short weeks of interference-free net access, the people of China may be far more reluctant to go back.