Unless you are using CPython extensions, PyPy is usable as a drop-in replacement that's significantly faster in almost all cases. In order to notice any significant speed gain, the JIT needs a chance to "warm up" though, so on short running applications or on web applications for the first couple of requests PyPy can be slower than CPython.
Personally I never used Python for anything other than glorified shell scripts and Websphere installations (after Jacl got replaced by Jython).
For everything else I prefer languages with type inference and availability of native compilers (AOT/JIT) in their toolchains.
How good is PyPy for production code nowadays?