I like the export/import patches a lot and used it quite a bit, but there was lately a situation which showed me that it can also cause trouble.
The problem was that I had a file f move from directory d1 to d2. In a next step that same file was renamed to fnew.
The patch files correctly reflected what was going on, but importing them via MacHg lead to trouble since the rename wasn't properly handled. The file fnew appeared as a new file with f not properly removed from the repo.