Unfortunately widows:0 and orphans:0 are invalid css - values have to be >= 1. This doesn't appear to matter at the moment, but there's no telling which direction development will take.
And they don't always work - they seem to fix the problem on Sony readers, but on the Kobo mini long paragraphs are always littered with page breaks. Same goes for some Android apps I have tried, certainly Aldiko.
The problem appears to be caused by a combination of screen size and font size, neither of which are under the control of the designer.
Last edited by NedC; 10-31-2013 at 08:22 PM.