[Technopatra]

Yep the PDF file opens easily and you can even keep the layers, woohoo!

One note: for one of the ai files I tried this with, I got an error message saying something like "this file contains PDF objects that will be ignored". I clicked "ok" and it continued to convert, but those objects -- which I really needed -- disappeared. My easy workaround was just to copy & paste them from the original ai file into their own ai file, then printed *that* as a PDF and opened it without a problem in Omnigraffle. Easy peasy!