This is actually the continuation of my recent hgsvn review.
While hgsvn and another solution where able to help Mercurial work at Subversions repos too, hgsubversion outperformed them by far when cloning the Trac-Hacks.org repo (~8500 commits at that time) within less than 4 hours.
I'm running it over the last 5-6 months now on an almost daily base. All in all it's really a setup-and-forget tool, working transparently in both directions.
Only bug that I've encountered repeatedly so far is, that I'm unable to commit more than one successive changeset in a row. Every time I tried to commit two or more at once, the process got stuck always right after pushing the first commit out.
I figured out from the issue tracker that this is a known bug, but I've not seen progress on this lately.
So all in all this is a great product and I give kudos to it's developers for saving me a lot of hassle when working with SVN at the backend. Vote would be 'almost perfect', if not the issue found had so tremendous effect on my work-flow. Enabling the pushing of multiple changesets at once is a must-have, and I really hope to see activity regarding this.