Twitter user libneko has created a service that allows you to quickly check if an ISP is slowing down twitter or not.
To check, the service downloads an image from the abs.twimg.com domain that Twitter uses, and then calculates how long it took to download. It can take up to one minute to check, it says on the service page.
It took 29 seconds to download the image from the Meduza editor's computer in Moscow, downloading the image at a speed of 103.57 kilobits per second. At the same time, an image on the computer of another Meduza editor in Latvia loaded in less than a second at a speed of 57,692.31 kilobits per second.