1. Male hair adjustments only work for very, very specific hair "styles".
Just changing texture of hair isn't enough. The fundamental hairstyle, kinda of a modified pageboy-cum-mullet just can't be easily coerced into many common male hairstyles.
In particular, doing any sort of close-cropped (front and back) buzzcut, high-and-tight, cesear-style etc. cuts are extremely hard to do. The problem is the basic hair "shape" deviates too much from the head shape, and cannot easily be fixed in ways that I can find. I've managed to get something passable to a crew cut, but far from thrilling, and very prone to "skull-show-through" if I touch anything to try and get it tighter. Help?
There's also color issues with hair. The big problem is that the "wild color" hue adjustment at the bottom cannot be lightened or darkened in any meaningful way. Red can be added or removed, as can yellow (blonde), but it cannot be darkened. For people wanting true red hair (not "auburn", which is what the SL appearance calls "red"

One last question about hair: Hair is an object in the system, as are other "Appearance" items. They have named "morph targets" (to use Poser terms) for them, which are the existing sliders. For hair in particular, it would be very useful if we could define new hair shapes with their own sets of morph targets to go along with the different sliders.
I realize this would probably push the modeler's capabilities too far, but at this moment, if we don't want some mullet-like (or punk-esque mohawk/spiked style) hair style, we're truly stuck since we cannot create our own hair objects that adjust properly for their own shapes.
2. Abdominals and Obliques (e.g. who stole ours?)
I haven't looked at the female bodies yet, but I know on the male bodies it's very difficult to get a realistic lower abdomen. Part of the problem is that there's no separate adjustments to correspond to oblique & lower abs sizes (love handles are not obliques). This makes attempts at "cut" physiques look "off", and even makes "slight bellies" and extra weight but less than obesity kinda odd-looking.
Any chance we could get these base primatives for these muscle groups added to appearance, along with adjustments for their sizes (and perhaps tie visibility to belly as well)? It'd make more realistic male bodies (and female ones too I suspect) a lot more possible than what we can do currently.
3. Shirt ends slightly above where pants start?!
I've run into this problem quite a bit lately. There is no real overlap in the "shirt" design over the waist of the pants design. In "tall" proportions, in fact, there's a discernable gap between the bottom of the shirt, and the top of the pants. Can't we get some way to have the shirt extend a bit lower (and perhaps a depth control so it could be over or under the pants texture)? Right now, it's really odd-looking in a lot of attempts at "loose" shirts.
4. Somewhat similar prob to #3 with boots and pants
Another, similar problem I've noticed is that it's hard to do true high-length boots right now. The texture stops but the color keeps going. Which is fine in many cases, except that if the texture is showing lacing the effect is quite strange. It looks like the shoe and pants textures need similar texture overlap and depth control as the shirt and pants need.
5. Full-body skin textures?
I'm a little confused as to what of the skin controls will apply when a full-body texture is used, if the textures can in fact be "full body" (still experimenting here, so forgive me).
In particular, while for a custom freckle pattern, being able to turn them down but still have ruddy cheeks is nice, what about in the case of a scaled skin texture? Suddenly it seems all the existing red/pink-oriented adjustments will in fact detract and need to be set to zero, yet lack ability to completely replace using textures (shading control in particular).
This sounds like another case where having the adjustments tied to something in the texture (or multiple textures as named morph targets) is needed. I presume we're not gonna get that kind of thing any time soon?
6. How do we do <5 fingered hands, <5 toed feet, tails, etc?
Question says it all.
Any and all help appreciated, particularly with the hair stuff.