Has anyone ever had the feeling that they should tackle something strange...

Yep !

Like... writing an entire TCP/IP stack in pure Perl?

Nup !

I must admit that I once felt fairly smug about having written XS code that could out-perform Math::BigInt ... but then I looked at GMP and PARI (even OpenSSL), and the modules that wrap them ... and no longer felt so smug :-)

Cheers,
Rob