> if it's a project that isn't my day-to-day but is in a language I already have set up in my IDE, I'd much prefer to open it up in my IDE and use jump to definition and friends than to try to grep and hope that the developers made it grepable.

It's funny, because my preference and actual use is the exact opposite: for a project that isn't my day-to-day, I'm much more likely to try to grep through it rather than open it in an IDE.