I finally got around to buying some of that Soapnut hair washing powder we were talking about here (http://forums.longhaircommunity.com/viewtopic.php?t=2196). Tried it today before my henna, and I'm still sitting here with a head full of goo, so I can't talk about dry results yet - how my hair feels when dry probably won't say much about the soapnut powder anyhow, after henna and a C/O wash to get the henna out.

But I can say that I liked the washing procedure as such and the way my hair felt when wet and towel dried. I mixed about 1 1/2 measuring spoons (one measuring spoon equals about one rounded teaspoon) of the very finely ground powder with a little water to get shampoo consistency, massaged most of it into damp hair (roots and length/ends), let sit for a minute, massaged again, rinsed. Repeated with what was left, which was enough for the roots.

It didn't lather at all, which was okay for me. It's about as easy (or hard) to spread as Terressentials clay. It washed my hair squeaky clean, rinsed out easily, didn't seem to leave a residue, and my hair felt soft to the touch and easy to comb through afterwards. Apart from the lack of lather it reminded me a lot of MM shampoos, which means it would probably be too stripping (for me) to use constantly, but great for a thorough shampooing in between C/O washes.

INCI on the jar says:
Sapindus Trifoliatis, Azadirachta Indica, Hemidesmus Indicus, Adhyranthes Aspera (which is probably a typo and should be Achyranthes Aspera), Phyllantus Niruri

That would be Soapnut, Neem, Hemidesmus (whatever that is), Devil's Horsewhip (conatins a saponin), the last one is Amla I think?

The scent may be something you have to get used to - I personally liked it, reminds me of carob which I love the scent and taste of. The scent doesn't linger.

[Edited to fix typos]

Oooh, Madeleine, I don't know how I missed this post! That sounds like great stuff. Do post results as you use it again!

Bumping this to add new info (pasted out of my journal):

Today I finally used Manufactum soapnut powder followed by just an ACV rinse and conditioner. I had tried it twice before, but always before henna and a C/O wash to get the henna out, so the end result didn't have much to do with the soap nut.

I mixed a measuring spoon (about a rounded tea spoon) powder with water until I got a pretty runny mix. I had mixed a thicker paste before, but I wanted to see if it spreads better as a liquid (and it did). It even foamed a little which it had never done for me before.
Wet down hair, applied mix to the scalp and roots, massaged scalp, rinsed. I didn't specifically wash the length, but didn't hold it out of the way while rinsing either. Followed with a weak ACV rinse (about 2 table spoons ACV on 1 litre/quart water) and Nivea conditioner on length and ends. Let sit for a minute, rinsed, towel dried and applied Seal The Ends.

Like Fox wrote before, the soapnut feels mildly alkaline, as in raising the cuticle scales. Even after the ACV rinse my hair feels slightly rough (although it looks shiny). There's also some residue that could be mineral buildup (I did rinse well), and my roots don't feel as clean as I would like. My hair is quite fluffy and soft though. I've got mixed feelings about this ... so far I guess soapnut is okay for me to use every once in a while, but on a regular basis I'm pretty sure I'd get some serious buildup. Next time I try it I'll use distilled water for initial and final rinse to see if that helps. At least my scalp didn't protest.
I'm curious to see how long my hair will stay clean. My guess is that I'll have to wash again before my next scheduled wash day.
Out of the all-natural options I tried so far I still like MM best.

Two days later:

Ack. Just like I thought it would happen I had to wash today again, day two after the soapnut wash. In fact I already felt like washing yesterday, but thought I'd give my hair's condition another chance. Sometimes sleeping and brushing changes something. Nope, it stayed icky, greasy and feeling coated.
So I did the works today: C/O washed all over with Schauma, ACV rinse (a little stronger than usual), then Nivea conditioner on length and rosemary EO scalp massage. After drying my hair still felt sticky. Oh my, what did that soapnut stuff do to my hair I brushed and it feels sort of okay now, but still a little stringy. I'll make sure to use shampoo next time I wash, probably one of the MMs.

So, sadly, I guess this is not for me. It might work for someone who is knows how to deal with soap based / alkaline shampoos.
Maybe I'll try it once more with an initial distilled water/ACV rinse some time, but it'll be a while until then.