Hi there,
I am not sure which would be the preferred mailing list for this kind of a suggestion (wikitech, comcom, internal, this one) so I flipped two coins.
As far as I know, we are constantly blocking people when they are live-mirroring Wikipedia (instead of downloading the dump or negotiating a data feed). Apart from that, there is no consequence for the people running a live mirror. I remember at least one instance in which the person running the mirror tried to change IP addresses faster than they were blocked.
I can imagine that this is a time-consuming and sometimes frustrating effort. My suggestion would be not to block these IP addresses any more but to deliver slightly modified content to them, basically the same Wikipedia text plus a ad banner or Google Adsense box right above the text or next to it. That way, it would at least be of some sort of reward for the foundation running the servers...
What do you think about it?
Mathias