HIya, I also use the green eco balls by eco zone, they were the first environmentally friendly product i ever bought - my first set lasted amazingly over 3 years, we used to have 4 children living here so that was an awful lot of laundry and i definately used them far beyond their 1000 washes.
I have a new set now ;-) I like them, they do get clothes feeling clean and fresh and although they did struggle on some stains when my daughter was weaning (carrot, tomatoe) on the whole they are brilliant. Grease stains need a stain remover before washing but again, some washing powders don't shift grease stains - i think that if you want to be environmentally friendly, you always have to be prepared to put in the extra effort.
I mix between soapnuts and eco balls now, so i use the balls for all of my dark loads, bedding, towels etc and soapnuts for my whites although i go in phases of using soapnuts for a week or two. I could never go back to buying washing powder, not even ecover because i see washing powder as being a complete waste of money, i don't like the fact that the powder residue is left in our clothes and i can't stand carting boxes of powder from the market, nor the mess that i seem to make with powder ;-( I find it uneconomical and apart from ecover it is so bad for us and for the environment. I'd rather be vigilant with stains, treat them with a stain remover and put in the effort that way.
I wash my dh's dirty work clothes with the balls, he is a gas engineer so is always filthy from crawling under floors, kneeling in plaster etc, his clothes are always clean and sweat free and the fact that i can reduce the rinse cycles right down, my laundry is washed quicker with huge savings to our electricity bill - not to mention the water we save.
I don't see a few odd stains an issue when you can see the overall benefits.
anne