svnversion is the right tool for this job, as it scans the entire working copy and produces an appropriate summary.
I just checked that TortoiseSVN doesn't have the svnversion command. It has a SubWCRev command which works entirely different.
So, from where I stand now, I think it's ok to depend on svnversion being on the PATH on all OSes.
However, it would be too bad if we strictly depended on having Subversion available; especially if that would apply to our source code distributions. If we can come up with a scheme where we can prevent the version file from being overwritten when building from such a tarball, I don't see any issues with such a feature anymore.
Bye,
Erik.