Use as kindling, IMO. The worst computer-related book I have ever had the misfortune to encounter was from the "21 Days" series. It wasn't the Perl in 21 Days book specifically, but it was so horrifically terrible that I feel comfortable condemning that one too without looking at it. We're not just talking here about a book that excels in mediocrity, like the For Dummies books that present things in suboptimal ways, contain mistakes, and leave out important information. The "21 Days" book that I read was MUCH worse than that. It was the "warn others to stay away" kind of bad. Avoid, avoid, avoid.