Here's a great study by the Harvard's Berkman Center, estimating the actual usage of anti-censorship tools by Internet users in countries with pervasive website blocking.
Berkman estimates that 3% or less of the total Net population in these countries bypass censorship via web and http proxies, virtual private networks, or circumvention software like Tor and Psiphon.
The implication is that this is a surprisingly low figure, and that the unanswered question is why is it so low? Is it because these tools are hard to use, or is it because few see a need to use them?
I'd be fascinated to see even more research into these important topics, and ways devised to increase the numbers.
Even if a larger segment of the Internet population did have access to anti-censorship tools, though, the damaging effect of pervasive Internet blocking on journalists and the free press would still exist. It's not just the availability of particular news sources that makes for online press freedom in a country, it's the interaction and diversity of those sources. Even if you personally know how to reach a particular news story, you're not likely to link to it in your blog or your news site if you know that a sizeable proportion of your audience aren't going to see it - or that you'll be blocked if you do so. Circumvention tools are incredibly useful in spreading the news (and don't necessarily need a large userbase to do so), but they can only ever be a band-aid.