This very good question, just in from IFeelCook:
THE QUICK ANSWER: Tagging is not currently possible.
Please answer the poll below to let me know if you think a tagging feature would be useful on the site. Please also bear in mind that features are typically added at no cost to me only if there is sufficient demand across all of my developer's (Hoop.la's) sites/customers to merit the development efforts. So interest would need to be high here and elsewhere for them to consider any feature additions (thus the importance of answering the poll if interested).