Egon has an interesting angle on Peter Murray-Rust's observation that you can't mine PubMed Central:

I was wondering about this section in the CC license of much of the PMC content, such as our paper on userscripts (section 4a of the CC-BY 2.0):

You may not distribute, publicly display, publicly perform, or publicly digitally perform the Work with any technological measures that control access or use of the Work in a manner inconsistent with the terms of this License Agreement.

CC-BY 3.0 reads differently, but has similar aims. [...] Peter indicates that the NIH has put in place 'technological measures to control access' to the distribution of our work on userscripts (the PMC entry). That is in clear violation of the CC license. [...] What the PMC website should indicate, instead, is that text mining is allowed for the PMC OAI subset, but that they would highly prefer to use the PMC OAI or PMC FTP routes. This is the least they have to do.

No matter what, I still have the feeling that any technical obstacles are disallowed by the CC-license. Any legal expert here, that can explain me if the CC license allows controlling how people have access to my material?

In other words, can they do that? Like Egon, I await legal advice... how 'bout it, Creative Commons?