I'm currently using hg 1.4.1 with python 2.6.4 and subversion 1.6.6 to
regularly convert a local copy of the GCC svn repository (available via
rsync, cf. http://gcc.gnu.org/rsync.html) to a hg repository.  This is
running on a Sun Fire V880 with 6 1050 MHz CPUs, 12 GB RAM and local disks.
While the initial conversion took several days and a couple of restarts
(VM exhausted; I've been using 32-bit binaries), it finally completed.
I'm currently running regular incremental conversions after updating the
local copy of the svn repository.  Unfortunately, they are extremely slow:
although only about 30-60 revisions are added per day, the conversion takes
on the order of 12 to 13 hours.  I'm simply running

$ hg convert svn/repo hg/repo

I can hardly believe that this must be this slow.