Since Delicious is owned by Yahoo there isn't a serious risk of complete data loss, but it's better to have a local backup of your data than risk losing your account with no recourse for data retrieval. Since there are a number of ways to accomplish this, we'll cover the geekiest method today, which was derived from but slightly different from the article linked below.
Open up a terminal prompt and type in the following, replacing username and password with your Delicious credentials.
curl -k —user username:password -o backup.xml -O 'https://api.del.icio.us/v1/posts/all'
If you don't have curl installed, you can also use this wget command to perform the exact same task:
wget —no-check-certificate —user=username —password=password -Obackup.xml https://api.del.icio.us/v1/posts/all
At this point the backup.xml file should contain an xml representation of your bookmarks. You could even get really slick and schedule this as a daily or weekly cron job.
You can alternatively create a manual backup at any time by simply navigating your web browser to
https://api.del.icio.us/v1/posts/all, entering your Delicious credentials when prompted, and then saving the resulting xml to a file. Note: Instead of doing backups you could synchronise with your browser using the official Delicious extensions for Firefox or Internet Explorer.