Okay, here's a whole bunch of other links to ELISPOT-related sites, articles and directories.
An ELISPOT FAQ. It's somewhat company-specific, but still has a lot of general information.
Some info on frozen PBMC reference samples. The cryopreservation technique they used is pretty darned good.
An article which mentions the use of cytokine ELISPOT assays in diabetes research. These assays are also seeing increased use in oncology and vaccine development.