Our cytology laboratory in Rochester participated in a study with just such a machine. The company was called NeoPath I think (they've gone through a couple of name changes, so I'm not sure if they still go by that name or not. The name of the machine was the autopap). A couple of our cytopathologists were involved with the company. Anyhow, I'll try to explain how the machine works. Basically, the computer "learns" what a normal pap should look like by you, the end user, running a litany of "negatives" through. There are special algorithms in the machine that do this. I think you're supposed to put in a bunch of abnormal slides, too. Again, not sure of the exact numbers of each.
The autopap then "screens" each slide. The slides that it deems as negative are given a "No Further Review" classification, meaning that the cytotechnologist or Pathologist does not need to review the slide. Others are flagged for Review, or given an error code of some reason (i.e. there are large air bubbles, the coverslip isn't square on the slide, etc.). It doesn't "diagnose" the pap (so it cannot differentiate a Low Grade Squamous Intraepithelial Lesion from an ASCUS, for instance). If you use a special program with the machine, it will read the barcode on the sample, and take you to each area of the slide that was "flagged" as abnormal (somewhat similar to the now defunct Pap Net machines of a few years ago), or the cytotechnologist can rescreen it.
The machine was surprisingly good at detecting slides for "No Further Review", and indeed, it is FDA approved to do primary screening. So, you can technically have the machine call the slide negative and never look at it (but I'm pretty sure you still need to have at least 10% of those negatives "quality control" rescreened by another cytotech, just like the others).
While the machine was pretty good, I'm not sure when or if they will catch on. It may be the perfect addition to a small lab in an underserved area (like here in the Caribbean, for example, where cytotechnologists are virtually non-existent), but in our lab, it was more of a pain. Lots of error codes. If the slides aren't close to perfect (as far as coverslipping and staining), the machine kicks them out. I doubt a machine will ever be able to make a definitive diagnosis--especially an abnormal one. There is just no substitute for the human eye or human judgement. Even the coulter counters in hematology can only flag something as "Abnormal WBC (or PLT or RBC) Population". In the end, I think humans will always have to say just how "abnormal" something really is.