I was able to observe the same issue:
I'm using Python 2.6.5 on Ubuntu 10.0.4 LTS. My system is 64 bit Intel Core I7, Quad core, Linux kernel 2.6.32-generic x86_64, Ubuntu EGLIBC 2.11.1-0ubuntu7.5.
A simple client TCP socket, which sends 35 bytes over to a server on localhost and receives 20 bytes in response, produces only 22 RPS. An identical application written in C gives me 7000 RPS. TCP_NODELAY is on on the server side. Turning on TCP_NODELAY on the client gives me ~500 RPS in Python (which I'm satisfied with, 'cause I think I then hit other bottlenecks).
Still, such low performance on by default can be surprising and hard to debug.