It seems that Pogoplug's software now only provides synchronisation from PC Folders when the new Uploader is running on the PC, and the reliability is suspect.

As an alternative, I'm using Microsoft's free RichCopy utility set-up to run periodically using these instructions: http://www.symantec.com/connect/articles/how-replicate-file-shares-using-microsoft-richcopy . The results are excellent.