Thanks for those links!

Of the files that won't unstuff, there are 24 LimeWire Documents (mostly .sit, also a .pdf, and a .tx), 4 Stuffit Expander documents, 1 Stuffit document, and 1 Stuffit Deluxe archive.

The downloaded files that WILL open are:
1 ZipIt document, 2 SimpleText documents, 1 text clipping.

So maybe the files that won't unstuff are corrupt or incomplete? There are a lot of them though, doesn't seem likely to me.

I'm thinking there's something I'm not doing right to open them.

Besides the "error #17527, Insufficient access privileges", there were a couple of Stuffit files that when I tried to unstuff them said: "The file xxx.sit does not appear to be compressed or encoded. The application LimeWire might be able to open this file."

I tried this, but there is apparently no way to open a file in LimeWire.

Surely this is a common problem? If it is, no-one is talking about it.