I ran into a problem with an RSS feed that I added this morning. I was able to see the available files, but downloads for all of them failed. I did a little snooping and found that the URIs in the RSS had embedded spaces. Juice was passing the derived URIs as-is to the web server and was getting back an error since the web server would not accept the URI with embedded spaces.
The root of this problem is obviously the fact that the publisher is providing URLs that violate RFC 1738, but it would be very useful to have an option in Juice to "groom" the URI by escaping any illegal characters before requesting the file. My feeling is that this should be optional, with a checkbox in the preferences that is unchecked by default.