It is best to experience this cool application yourself, so, I will just extract some excerpts from their own words below.
del.icio.us direc.tor is a web-based rich UI for del.icio.us. It leverages the XML and XSL services of modern browsers to deliver a responsive interface for managing user accounts with a large number of records.
The main features are
- In-browser handling of del.icio.us bookmarks (tested up to 12,000 records)
- Find-as-you-type searching of all your bookmarks, with basic search operators
- Sort by description, tags, or timestamp
- Ad-hoc tag browser