I think cargo supporting binaries and sharing build dependencies between projects (cf maven's .m2 directory) will mitigate a /lot/ of Rust's build time issues.
It brings the cost of trying an idea out down considerably. I've had a few times where I think "i know, I'll just try this idea out" and then I make a new project, add a few deps in Cargo.toml, hack some code, and then build. Oops, the first build takes half an hour. Then I think I should try new ideas out in Go or python. Alas.
