The name of course comes from a misunderstanding of French, dent de lion meaning tooth of the lion. The French really should speak more slowly to English people. The ubiquitous yellow flower also goes by some pseudonyms; the French pissenlit and the English piss-a-bed. This is a little hint as to one use for the plant. It was popularly used as a diuretic. The leaves can be eaten in a salad, the roots and the leaves were used to make herbal remedies to flush out the kidneys and to treat gout.
The milky juice of the dandelion is said to cure warts, this seems a preferable method to putting a toad in a bag which is then hung around the neck of the warty fellow until the toad dies. It was also claimed that dandelion was helpful for easing the effects of rheumatism.
During World War II, when the British were rationed they used dandelion roots to make “coffee”. The soft drink Dandelion and Burdock originated in Britain during the Middle Ages as a flavoured mead. It has a similar flavour to sarsaparilla, apparently.
The flowers are a source of nectar for bees, butterflies and moths. As well as attracting pollinating insects, dandelions release ethylene gas which helps to ripen fruit and they also have a deep taproot which draws up nutrients for other plants.
The yellow flower turns into the fluffy seed head for dispersal in the wind. This gives rise to the German name Pusteblume, meaning blow flower. Before technological gadgets, children would keep themselves amused by blowing the seeds off the plants.
These seeds are not only eaten by birds, but are also used as nesting material. This site here gives more information about the benefits of dandelions to wildlife, with some fantastic photos too.