Personally, I have not used them. I like relays for marginally meaningless reasons. But the SLOClone forum guys use optoisolators alot for channel switching because that's what the original SLO used. If you don't get alot of info out of here, that may be a place worth looking.
That aside, it's interested to see the price difference between Newark and Allied (the only two places I found that carried the VCT5C3), $7.38 and $2.50, respectively. Looks like it's worth looking around for a solid price.