I'm doing a bit of research for a couple of book proposals, and I definitely know what I think but I'm not the sort of person who buys technical books (I get them all for free, and in multiple copies sometimes!). The difference between what I think and what people will actually buy can be apples and oranges.
Various editors tell me that tech books don't sell well (where "well" probably means in comparison to Grisham and the like), but that the ones that particularly tank are the ones the start with "Perl &". Allison talks about the spike in Perl book sales this summer due to general purpose Perl books, and with her special editor superpowers, she knows which books do better than others.
So, let's say you've read the Llama, the Alpaca, the Camel, the Panther, the Ram, and so on. Are you still looking for something? What haven't you found that you wanted?
If you're not the sort of person to read books, what do you wish other people would read in books (perhaps so they didn't start all sorts of fires in the workplace)? In the alternate universe of unlimited tuits, free rent and food, and 70 degrees F everyday, what would you put in the Perl book that you would write?