PhillyGirl swears by her formula, and others have reported various levels of sucess on the Web.
Thing to keep in mind is basically one is going back to the way our grandmothers and great-greatgrandmothers did laundry.
Soap, washing soda and borax will indeed get one's clothing clean, but the formula lacks modern chemicals that were the reason women dropped pure soap for laundry once detergents came upon the scene.
Lack of optical brightners can lead to whites and colours turning tattle-tale grey. Certian stains simply cannot be shifted without enzymes. Pure soap is hard on many washing machnes, and will cause gunking up and mould problems unless the chemical mix of water softeners is in measure to soap.
Without "washer protection agents", certian parts of the machine could suffer with repeat and or exclusive use of homemade brews.
Soap needs warm, to hot to boiling water to really work well, and several hot or at least warm rinses to get the stuff out of fabrics.
Being as all this may, there is no harm in whipping up a batch and giving it a go. Personally recommend reducing the amount of washing soda and borax in favour of phosphates. Even back in the day, vintage laundry manuals advised housewives of the benefits of using phosphates over washing soda.
Finally, if one is going to go this route, vintage Fels Naptha is the soap to use for all but delicate textiles. The small amount of petrol (Naptha), helps shift soils and grease, while it also contains OBAs and other goodies that made it the "detergent" of it's day.
Next in line would be Kirkman's Borax Soap. No longer made, but have a nice sized stash, however one can often find bars someplace. The borax in this soap gives laundry a fresh clean scent, and it shifts soils well.
L.