If you’re in Japan and don’t know Japanese, unfortunately you’re usually hosed unless you’ve got a special arrangement (embassy/company work where they speak your language, international exchange program, etc.). Fortunately, if you’re learning Japanese while you’re there, it usually comes pretty quick despite how difficult it can be to master- being thrown headfirst into a situation where you can’t survive without a certain skill will do that to you.
When I was in an exchange program, I joined the school’s Aikido club without knowing much Japanese at all, and over 6 months I went from communicating mostly through hand gestures to understand most of what everybody can say (and being able to discern any words I didn’t know through context or being able to ask what it meant). I’m a lot better at Japanese now than I used to be… but I don’t live there anymore :(.
Japanese internet is pretty awesome, but surprisingly there are a lot of “dead zones”… sort of like how FIOS is super awesome for everybody in the USA if it’s actually available. I know that outside of the bigger cities it can be surprisingly hard to find internet hotspots and fast connections and etc. Another bonus here is that I feel a lot of Japanese people aren’t as proficient with the internet and computers as they might seem- I have a ton of friends there who were surprisingly out-of-the-loop when it came to doing anything with a PC outside of Microsoft Office >_>.