Don't worry, I am still going to persevere, and I really liked books 1-4, but I just read books 5 and 6 in quick succession and maybe that was too much all at once.
My problem with Definitely Dead (book 6) had more to do with the unpolishedness of it than the demons appearing. There were tons of grammatical errors, and she used the phrase "definitely dead" about a million times.
I read a review where someone was complaining that she is introducing too many new characters and leaving out the old favorites. I agree fully with that, I mean, Bill hardly makes an entrance in book 6 and the new love interest, Quinn, is really flat as a character.
Anyway, that's just MHO. I tend to get tired of a particular style (in this case romantic fluff) after a few books and need a change. In a couple of weeks I'll read book 7 and hopefully her editor will have done a better job.