Sheldon:

Jackson frames have always had a bit of a mixed reputation in the United States. Reality, I believe, is somewhere in the middle. Some Jackson frames are absolutely gorgeous and show nice workmanship. In some cases, though, sloppy mitering and less-than-perfect attention to detail give the detractors some valid ammunition for criticism. Even examples that display a few shortcomings are usually quite nice overall - so if you find yourself drawn to the seductive looks of a Bob Jackson frame you probably might as well go for it. Bob Jackson also constructs frames under the Merlin label, not to be confused with the completely unrelated titanium frame manufacturer.

For a great article on Bob Jackson see the book "The Custom Bicycle" from the late 70's. A friend of mine has a Jackson that he has owned for years. It truly is one of the most attractive bicycles I've ever seen. It features great stove enamel, fun contrasting red panels, and rides great. Lots of Bob Jackson frames entered the country through the big mail order houses, so while not totally commonplace these days there are plenty to be found. They were never terribly expensive - and aren't terribly valuable now. For a really nice N.R. bike in guideline condition a value of $800 to $900 is probably fair.