Don't know about hg, but `cvs up -dP' gets it done on case-
INsensitive HFS+ volumes on Macs I have.

Source sync tool of preference aside, I can second rog on case-
sensitive HFS (or even Mac(NeXT) UFS if you like). Since both of
these can be less convenient on boot volumes, a partition for the
purpose, or a removable of some kind so formatted, is handy, since
the filename case issue comes up in more than just p9p.

-Josh