You might want to spend a little time with miTaggedMarks. It's the closest thing to Powermarks. Michael has put a lot of thought and work into the program, and his tag handling is actually more sophisticated than that of Powermarks.
I recently uploaded the latest version (2 beta2) of miTaggedMarks (www.miTaggedMarks.com).
Main new features in version 2 are
- build your own toolbar for miTaggedMarks in nearly any browser, using bookmarklets.
- Combine tags with boolean operators (AND,OR,NOT) in an innovative easy-to-use interface, with immediate feedback,
and especially for (ex-) users of PowerMarks
- a more PM like search facility, with search for several text fragments.
- improved import from PM
See website or help file for the full list of new features and improvements.
Suggestions for further improvements are welcome.