I think I read somewhere that they start processing applications in groups, and only move on to the next group when all apps in the first are done. Maybe that's why there are such big differences in processing times? It would explain why there is a bunch of updates at once and then nothing for a while.
When my husband and I started this process, we went into it with the expectation and acceptance that it could be a full year before it was over; giving up after 2 months seems very impatient and almost suspicious to me. Chill out, people!