[nazgob]

This is interesting. As a Polish native speaker I can understand quite well other western Slavic languages (Czech and Slovakian) and I'm not bad with southern Slavic stuff (Croatian etc). But Ukrainian or Russian is quite hard, maybe a word here and there (often with different meaning!).

[V-2]

Belarussian is fairly easy, too - not as close as Slovakian, but somewhat more similar than Russian or Ukrainian. It's rarely heard though, as most of Belarus speaks Russian, especially in cities.

[mootothemax]

Hah, I always think that Ukrainian is just like Polish, albeit spoken with an Italian accent.

(although I know there are plenty of false friends between the two!)

[V-2]

Well, not to me it isn't (native Polish speaker)... Yes I can sort of, kind of, figure out what they're saying, but it's probably 50-60% plus some intelligent "cheating" if the context is clear