took over the seo role for a site using "+" as a separator.
convinced them to change to "-" ... even though that meant changing >90% of URIs the site has improved in longtial rankings and is generating a lot more traffic since then. However, some other changes were made at the same time; but the + to - switch was definitely helpful. I left the + separator live for one sub-cat to use as a control. It wasn't important for the site, so they were happy with not having to change the URIs. Other changes were made though. After normalizing traffic values that section seems to get ~10% less traffic in contrast to what other sections gained... but the section is so small, and get's so little traffic compared to the other sections on the site that it is very hard to get accurate data.