Like many of the other contributors to this thread, I was passionate about Powermarks. I used it and loved it for more than a decade. Last year, however, the developer announced that Powermarks was being marked for "end of life," and there would be no further versions. Fortunately, at about the same time I learned this, I discovered
Linkman. After some initial annoyance with some of its features, I found myself actually PREFERRING it to Powermarks! It lets me do more varied and sophisticated searches, and its checking for dead or moved URLs is both much faster and more accurate than Powermarks' was. Though you CAN organize your bookmarks into folders, you don't have to: you can use Linkman the same way you use Powermarks. Also, as has already been mentioned by others, Linkman has an "import from Powermarks" feature.
I might mention that Linkman is available as freeware as well as in a modestly-priced commercial version. Since I love Linkman's link-checking ability, I'd opt for the commercial version, but most of its other features are available in the freeware version as well.
The Linkman developer is continually improving this already excellent program. I've found that he's also very open to suggestions.
In short--I'm even happier with Linkman than I was with Powermarks. :Thmbsup: