I'm enjoying the autopuzzles, and most are really tough. I have a lot of car books, and even then, few clues to look things up.
The thing that really keeps baffling me is how a puzzle that seems like a piece of cake to me, is just unsolvable to others. Like my puzzle #7, which was one of the first I posted, and still sits unsolved in the Pro section. Now, most puzzles I put up here now (in the Expert and Pro sections, anyway) are cars I hadn't heard about before I actively started searching for difficult puzzles, but that one was one that had been left on my harddisk for several years - and now there hardly seems to be any information about it at all, even though it comes from a relatively well-known manufacturer. And then, I post some obscure car that I had never heard of - and within minutes, three people fight to give me the answer...
So, as I said months ago in connection with one of my puzzles that I thought was difficult, but proved to be ridiculously easy: I guess it all comes down to which books you've read and which web pages you've visited...