- Managed (GC-ed) pointers are moved to the standard library. There is no special syntax (formerly `@`) nor special header (for vectors containing managed pointers) required.
- Special treatments on `str` and `[T]` vectors are being generalized ("Dynamically Sized Types").
- Lifetimes of temporary expressions have changed in somewhat more intuitive way.
- Syntax extensions are now exportable, documentable and much more flexible ("procedural macro").
- Language simplifications: `do` syntactic sugar is removed, `priv` is now default, no trait bounds by default (e.g. formerly `:Send` was implied for `~Trait`).
- The smart pointer usage has been improved with new `Deref` and `DerefMut` traits.
- There are now many auxiliary standard libraries instead of a single `extra` library.
- Usual library fixes, redesigns and influx took place. Most prominent change is an introduction of growable vector type, `Vec<T>`, which subsumes the original `~[T]` type.
- Rustpkg is gone, long live Cargo! Rustc has also combined many related options into umbrella flags (e.g. `-C`).
As prior point releases of Rust did, Rust 0.10 does not represent a significant milestone. It is always recommended to use the most recent development version (master) of Rust, but it had been a great undertaking to compile Rust from scratch. From 0.10 onwards, however, there are official nightly versions [1] and brave souls can play with master more conveniently now. (They are currently not signed yet, so take that in mind.)
[1] https://mail.mozilla.org/pipermail/rust-dev/2014-March/00922...