I've been knitting circularly for many years, but there's always something new to learn from Margaret Radcliffe. This isn't really a pattern book, it's a teaching guide and reference book, with many useful techniques and tips, and comparisons between various methods for different aspects of circular knitting, from cast-on to bind-off, and including a basic introduction to knitting on two circulars, double-points, and magic loop. There are patterns, but most of them are teaching patterns, to help learn a new technique. However, there are some excellent if simple patterns for full-size projects; e.g., she shows how to knit circular shawls both from the center and from the outer edge. And she has a very good section on how to adapt stitch patterns from flat knitting to circular, with samples ranging from simple knit-purl patterns to cables and slip-stitch designs. One moral I took away already: as much as I hate to seam sweaters, some stitch patterns are really going to be easiest done flat and seamed.
Highly recommended.