Sorry, I'm not equipped to publicly elaborate in detail. I have scattered bits of somewhat worrying information but can't present the total picture. I am hoping some more capable researcher would explain the current vital facts for us, now as Yandex is becoming of importance in the West. Yandex' bots have been hitting my sites (Europe and English) quite conspiciously for at least a year. There have been many threads on Yandex on WebmasterWorld, but some of them are less recent. Yandex does have a guide for webmasters, but it is in Russian. Needless to say: if you are active in Russia you have to play by Yandex' rules, not Google's, so in that case too it would be important to know them.