The problem with bookmarking applications is that aside from a few websites you visit regularly, browsing and searching your bookmarks isn't going to be substantially different from browsing and searching the web, so you can just as well do the latter. If somebody came up with a revolutionary new way to browse bookmarks, then this would also be a revolutionary new way to browse the web (or your filesystem, while we're at it). Whatever you come up in terms of search, however, has to directly compete with the quality of Google's search engine.