Mentostop (Russian милиция (police) =>менты + автостоп) is a funny and extreme way of hitchhiking. Mentostop is effective in some poor countries with very strong police and military aspect. Could be extremely effective after terrorist attack and less effective after peaceful period. In fact people in unstable countries tended to help or save another crazy foreigner crossing their land from another terrorist attack. Why should you refuse them? Let the people feel them as a part of helping process.
Before ask a policeman be sure that your documents are completely OK.
Former Soviet Countries with effective Mentostop
Better to know at least elementary Russian language.
Police in Uzbekistan are most kind and helpful among all Central Asia (2010). After checking your ID always trying to get a comfortable bus for you. Distances up to across all country just wait for proper bus.
Every policeman is ready to help you on the road. Sometimes they just carry you to the next checkpoint and ask local policemen to get a car for you. Also could offer some food or give some money (up to 5 USD :)).
Since campaign against corruption was started policemen became friendly and helpful. Usually trying to get a bus for you. Lifts across the country available. 1000+ km is not a limit. Best way to get a ride for a nighttime.
In Mauritania, there's a police checkpoint every 20 kilometers or so. Most policemen are very helpful and very surprised to see hitchhikers, sometimes even too much so. For more information, see the article.