Honestly, this data should be free, and available to researchers who work on social tagging.

You should contribute your bookmarks to a public data set. http://bulk.archive.org has offered to host such data sets. Someone should build a webservice that allows you to easily share your delicious tags. If no one steps up, you can simply email me your export (turian at gmail), and I'll package up whatever I receive.

Here is a delicious data set, for those who are interested: http://arvindn.livejournal.com/116137.html

I have some other social tagging datasets in my file. Let me know if you'd like me to dig them up.