I think my favourite thing about comfrey is the name. It's one of those words that is pleasurable to say. Say it out loud - comfrey. Com - frey. Ooh, lovely.
It's also a very useful plant. Its deep roots bring up nutrients from the subsoil, especially potassium. Think of it as non-smelly manure you can grow. You can add the leaves to your compost where they will speed up the decomposition in much the same way as fresh farmyard manure. You can stick bundles of leaves in a bucket and cover with water where they will rot down to a really foul smelling "tea" - you then dilute it to the colour of black tea and pour it on hungry plants as an organic plant food (you can also do this with fresh manure - see what I mean?) Or you can just stick the comfrey leaves in a bucket with no water where they will decompose spontaneously to thick black slime, which is just an even more concentrated form of the same plant food. It absolutely stinks to high heaven, so the manure analogy continues. If you dig a trench you can drop comfrey leaves all along the bottom, as you would well-rotted manure, and then plant crops such as potatoes in there. Or if you are planting out a pot-grown plant or seedling you can shove a comfrey leaf or two in the bottom of the hole. And you can lay a few leaves around your seedlings where they will act as a mulch to prevent water loss and enrich the soil - just like well-rotted manure. This is especially helpful for tomatoes which guzzle the potassium. Don't feel afraid to cut as much as you need - even as far as cutting back the whole plant. It will regrow with amazing rapidity, and seems to come back stronger every time.
It's clearly invaluable to an organic gardener, but it is also prized for its healing powers in humans. One old name for it is "knitbone", and scientific research has confirmed that it is beneficial in bone disorders. However it must not be taken internally as it can have very bad effects on your liver. If you come across any old herbal remedies that advise you to drink it as a tea for example, you should know that this is now considered a very bad idea. But preparations of comfrey for external use, such as oils, ointments or the fresh leaves, are used for skin conditions such as acne and rashes, for bruises, and for broken bones and sprains.
So why is this "weed of the week"? Why not "Very useful and beneficial plant of the week"? Well, if it's growing somewhere you don't want it to - bad luck. It's very hard to get rid of. Its deep roots which give it such useful properties also mean you'll have to dig an enormous hole to get it out. The roots are very brittle, so if you don't dig a deep enough hole, you'll snap the tap root and leave a bit behind. And sure as God made little apples, this will regrow. Don't think you can just cut it back either. As I said earlier, the more you cut it, even cutting off every leaf, the stronger it seems to get. It doesn't spread terribly fast, although if you let it set its pretty purple flowers, seedlings will appear. Deal with them quickly before they establish.
The best approach seems to be this one: if you have comfrey growing in your garden or allotment, declare that place to be your "comfrey patch". Erect a little sign if it makes you feel better. Fence it off if you like. Consider yourself lucky to have a healthy comfrey patch, and don't neglect to make much use of it. Because you probably couldn't get rid of it even if you wanted to.