I'm a confessed PyPy fan, and with version 1.7, PyPy has done a good job - the memory leaks of version 1.6 seem to be gone, and you can now run long-running processes (like a Tornado web server here in the post) with it. Especially for more complex template engines and situations where you work internally with larger data structures to produce results, it's a real alternative - but remember, PyPy needs more memory for the same work.