I've taken my delicious bookmarks and parsed them in various ways to analyze the tag structure.
To start, here's a sample bookmarks file. (Unfortunately, I don't put a raw version of entire file out on the web, as it contains some private information, such as people's email addresses.) Then here's a simplified tab-delimited text file dump of my bookmarks as of 31-Oct-2010. I've re-arranged this into a big grid that gives one an overview of all my tags (xlsx, xlsb, txt). (These are big, sparse matrices.) Here's picture of the top, left-hand side of the matrix.
[[* tags31oct *]]