At first this sounds silly, but as long as there is a other field possible, a validation section makes sense for single response questions too. The "Numbers only for 'Other'" option is a bit of help but a validation section would better.
I don't see a workaround for the validation function in that case.

Maybe that's a good feature request. For the time being, you will need to validate "Other" with JavaScript. Details of the script would depend on the validation requirements.

tpartner wrote: Maybe that's a good feature request. For the time being, you will need to validate "Other" with JavaScript. Details of the script would depend on the validation requirements.

With feature requests I got the impression that it won't make sense to submit them till LS 3.0 hits the scene.
The codebase seems to need a refactoring to allow adding more features without raising to much concern about the existing code. I might be wrong, but currently you seem to be the man for new feature Perhaps you should offer a DVD with the title "Mastering Limesurvey and add features with Tonys workaround toolbox".