You can make surprisingly significant gains by writing a TCP/IP stack that is intended for one process only. OSv is a kernel that supports a single process. By running memcached (just as one specific example) on OSv in KVM, you get better performance than by running it on the host. The trick is their network stack is significantly simpler and bypasses the kernel to go straight to the hardware. If you could do the same in user space, that's where you'd get your gains. (But I do agree with you - JUST moving to user-space is rather pointless).