I couldn't get to www.climateaudit.org, www.wolfram.com, www.wolframalpha.com, blog.wolfram.com, skydrive.live.com, and pretty much everything in those domains, including the Mathematica's WeatherData functions and similar stuff. Of course, a proxy was enough to circumvent most of these problems.
While the pages were not loaded, Google Chrome sometimes used to complain about the following error:
Error 101 (net::ERR_CONNECTION_RESET): Unknown errorMy Internet provider was able to provide me with the right solution, within a few hours. Something has changed about the format of the packets. So the Maximum transmission unit (MTU) had to be lowered from 1492 bytes to 1460 bytes. I suspect that another possible subtlety was allowed in the packets that can occupy up to 32 bytes.
Click the screenshot to zoom in.
To change the value, connect to your modem, e.g. via 10.0.0.138 or whatever is the right counterpart for your modem. It is a web page "stored" directly in your ADSL modem. Unless you know otherwise, the username and password is going to be admin - both of them. You find the menu SETUP / Data, or something like that, and change MTU: 1492 bytes to MTU: 1460 bytes.
In the case of my modem, the critical place is highlighted by red ink in the screenshot above.
Click Apply, and/or Save. Disconnect from the Internet and reconnect to the Internet, in a "software" fashion. You don't even need to reboot - but rebooting may be OK if you don't know how to disconnect more peacefully. And all the servers should be instantly working.