I think about toning in much the way I think about colour in an image. If it enhances the image, it's good; otherwise, not so good. If one is trying to replicate the mood of a print from a bygone era, then sometimes toning may help, for example.
In Jeremy's image, to me the color may slightly enhance the image, but it doesn't feel essential (to me). Toning in this case just seems like a weaker version of the color, so for this image I would go for the straight, untoned B&W version.
That's my qualified prejudice.