Since the last difficulty change, my average has been consistent with the theoretical average I've calculated. I use "Share-based". However, before the last difficulty change, my average dropped so low for such a long time that i had to switch to Pay-Per-Share until the difficulty changed. It was a bit suspicious, but I'm not someone who throws around accusations, especially if i had some really good days with that pool, and also that i had problems with my computer during the second half of that change. I'll monitor it during this difficulty, if it happens again, I'm switching pools altogether, especially that my hash/s is stable since the last change.