I'm quite an authority on all this, as I actually (and yes I'm quite sad) did a test in my washing machine. Put stains including ketchup, cooking oil, turmeric etc on 4 identical pieces of muslin square and then used soapnuts for one, ecover for another, washball for another and just water. ecover and water came out the same! wash ball was the best, followed closely by the soapnuts.
I have to say that you need to wash at 40 degrees, you really can't get away with 30. If I need to use a softener, I put white vinegar in the fabric softener drawer, along with some essential oils. washing doesn't really smell much, but certainly doesn't smell of vinegar. DD suffers from ezcema, but I've found it's cleared up completely since washing like this.
Another thing I do is to wash towels once a week at 90 degrees. the washing machine repair man said it really helps to keep your machine running efficiently and for longer, so the extra energy used hopefully will prolong the life of the machine.
For really dirty stuff, I either soak them first in soda crystals or rub things like collars with fairy soap. the only thing I have a problem with is fatty stains, so I do use a little "proper" stain remover.
So it's not entirely green, but certainly saves using a whole load of detergent and also saves a lot of money.
Hope this helps.
PS noticed today that Kleeneze are selling washing balls at only £5 so a good opportunity to try one.