Forgot to update on my hair and the whole not washing with shampoo thing. I'm halfway through week 4 now. At the weekend I used oatbran - you're actually suppsoed to use oatmeal but it's essentially the same stuff as far as I know and I wasn't about to use my lovely organic porridge when I'd bought the bloody oatbran anyway. You scrub dry hair and scalp well with it and brush really well to take it out again. It does make a bit of a mess but I think this was partially caused by the fact that I'd taken my glasses off and so couldn't see when I was making a mess anyway. This worked really well and I was pleased with it although I felt I'd done a much better job on the long part of my hair than the scalp simply because it's much easier to get at. After brushing out the oatmeal you rinse with hot water to get rid of any lingering bits. My hair looked good after this and felt good too, if a little thick.
On Sunday I decided to try the mayonnaise conditioning treatment. What can I say but that it was a disaster. First of all I should point out that I don't like mayonnaise and don't eat it. So sitting with the smell of a headful of the stuff wafting down to me for almost an hour wouldn't rate highly on my list of fun things to do. I couldn't hold out for an hour so after about 45 minutes went down to wash it out with some very hot water. Seemed to work okay and my hair did feel silky smooth. That was about ten o'clock. Left it to dry naturally, as I do most of the time. Went to market (smelling a bit like a salad sandwich) and then drove down to Arklow (about an hour's drive) for choir competition. Met choir for lunch and then went off for practice before competitiong at 2.45. A couple of people gave out to me for coming out with wet hair and I thought to myself it was a bit strange that at 1 o'clock it still wasn't showing signs of drying (it takes a long time but more than two hours when it hasn't been tied back is a bit much). Finally realised that it wasn't so much that it was wet as that it was greasy. Yuck. I don't think my hair has ever been that oily. I tied it back and made it through the day (we won our plain chant competition so that was good). As soon as I got home I washed it in very hot water again. I really didn't want to have to use shampoo.
Next morning I woke up with unbelievably matted, greasy hair. This is the kind of thing I'd expected to gradually happen over a few weeks before my hair sorted itself out but not overnight so I'm very happy to attribute it to the mayonnaise. Tied back but looking a bit terrible in work all day so when I went home I tried washing it in a mixture of vinegar and hot water, rinsed with lots and lots of cold water (so much for cutting down a bit on my consumption of water!) and it felt a bit better although I'd now switched smelling like a salad to smelling a bit like a bag of chips liberally drenched with vinegar. Tuesday moring I woke up with still very greasy, although slightly less matted hair. Another day of feeling icky in work. Yesterday eveing I decided to try the oatbran thing again although this time I just did the dry version and didn't rinse with hot water afterwards. There was definitely some improvement but again mostly on the long part of my hair and the scalp is hard to get at with the oatbran. This morning I washed well with hot water and for the first time this week feel like I'm almost approaching normal.
I'm very disappointed as I'd heard good things about hair being left in great condition after using mayonnaise. All I can say if that it didn't work for me!
Edited to add: 6 years later - update on not using shampoo