I'm planning a 4-5 month backpacking trip through most of Europe. Do 3 month Eurail passes cover local metro trasportation?
In Germany, Eurail passes cover all DB trains, which includes almost all S-bahns (I believe that most S-bahns in Berlin are not operated by DB). For all other transit, U-bahn, streetcars, buses, the pass will not be valid.
Go to www.eurail.com and look under "bonuses" for each country.