The primary legacy of Unladen Swallow (this was something that everyone agreed on at the VM summit at PyCon) were: a) improvements to LLVM for all users of its JIT, things like valgrind and GDB integration, lifting that 16 MB of machine code, and fixing various bugs, b) developing a cohesive set of benchmarks for the Python community, and c) drawing more attention to the idea of a fast Python.