I've been trying a fair few leaves recently - based on my old (circa 1977) copy of Food for Free. On the whole, I'm finding everything very bitter (maybe that's my sweet tooth showing!) and not too pleasant to eat. Perhaps I need to develop my palate a bit more - or mix these things in a stew /salad or something to bring out the mix of flavours (or mask them!).
Dandelion leaves - I found too bitter to eat and enjoy by themselves. However, I have made some dandelion, burdock and nettle beer which should be ready for drinking this weekend.
Dandelion root coffee - I can see why it is called a coffee substitute (smell and taste are vaguely similar to coffee) and I did drink a cup of it but felt I had to finish it because I had spent a lot of effort digging up the roots and roasting it. Started to feel a bit queasy after finishing it.
Nettles - I haven't tried eating them yet, but nettle tea (three nettle tops steeped in water for about 10 minutes) was OK - but smelled very strongly of guess what: nettles! I'd probably prefer it with something else mixed in, but it wasn't bitter.
Wild Chervil (cow parsley): a leaf by itself was fairly bitter - but then again I believe it is more generally used as a flavouring. I guess that if I tried a leaf of sage or something similar from the garden that it may well taste bitter too.
Hawthorn leaves - Richard Mabey describes them as having a 'pleasantly nutty taste'. I agree with matt-w - they taste bitter to me. I tried some hawthron flowers yesterday and they were slightly better - maybe I'll try the leaf /flower tea.
Hawthorn berries - I'll have to wait until later in the year for this, but I saw Ray Mears in his recent programme squeeze out the juice from the berries, which jellified into a sort of cake and he then cut it into slices and dried it and it formed a sort of fruit jerky - he was eating a piece that he said was three years old.
Wavy bittercress - I found a big patch around my compost heap and this was nice - it really did taste like cress and I enjoyed eating it.
Cornsalad - there's a patch in my garden but I haven't got around to trying it yet.
Hedge garlic - I believe that this would normally be mixed in with something, but I found that chewing a leaf wasn't too bad - a reasonably pleasant garlic taste.
Willow twig - tried chewing this to see if I could throw off a mild headache - now this really is bitter. But is isn't meant to taste nice!
Geoff