From a user perspective, if you create a series of interconnected maps (a map chain), the general belief is if you put those maps into the bump channel of a material, the greyscale of those maps will define the bump, black being bumped in, white being bumped out. However, this is not the case. Many maps do not produce proper bumps, which does a number of things. It limits the choices the artist has when it comes to making bump maps. It generally means that you can't just copy the diffuse map into your bump map because you may have used one of these maps in your map chain. It forces the user to resort to things like texture baking to get a proper bump map, which can be time consuming to render, setup uvs, and then keep around a lot of baked out maps (this is especially bad if you have thousands of objects).

Here's a list of the maps that produce incorrect results...

1) Vertex Color: If you take a surface, change some of it's vertex's to white, and some to black, then place a VertexColor map in the bump slot, it produces no results. This means that tricks like the following cannot be used to produce bump maps.

2) Mix map: Make a mix map, have the two colors be White And Black. In the mask slot, place a noise map. The result visually in the material editor is black and white noise. However, if you place it in a bump slot of a material, it does not produce a noisy bump.

3) Color Correction: If you use a Color Correction map to darken or brighten an image, the bumps do not get bigger or smaller. This means if you're using a Color Correction in a map chain in your diffuse map channel, you cannot copy that same map chain into the bump slot, since it will not create the expected results.

4) Mask: Like mix, mask also doesn't work, so if you place a simple color into the map slot (like from a bitmap), then place noise in the mask slot, you get no bump even though the greyscale appears noisy.

5) Output map: Turning up the Output amount on the output map will cause the colors to get brighter, but the bump won't get stronger.

6) RGB Multiply: If you take a noise in slot 1, and turn the color for slot 2 to black, the resulting greyscale is black, but the bump still exists.

7) RGB Tint: Same as RGB Multiply.

Ideally, in max, the bump map would look identical to the greyscale of the maps that make up the bump channel.

A very common workflow when making textures is to keep multiple groups inside of a single photoshop file. Say you have unwrapped a model, and you are painting a color, bump and spec map. Inside a photoshop file you may have 3 groups set up, each with multiple layers, one group for color, one group for bump, one group for spec.

Lets say you're working on the color map, and you've painted 3 layers inside of the color group, here's the current workflow for saving your file and loading it inside of max...

1) Turn off all the layers inside of photoshop that don't relate to color (bump and spec) (2 mouse moves, 2 mouse clicks)
2) Shift-Ctrl-S for "Save As" (3 keys)
3) Uncheck Layers (1 mouse move, 1 mouse click)
4) Change the format to Tiff (2 mouse move, 2 clicks)
5) remove the " copy" from the bitmap name (1 mouse move, 1 mouse click, 5 keys)
6) Add a passname to the file name, like for example Color (5 keys)
7) Hit ok (1 mouse move, 1 button)
8) Change any Tiff options you need (maybe 2 mouse moves, 2 clicks)
9) Hit ok (1 mouse move, 1 click)
10) Hit Yes to the "Do you want to replace the old file" dialog (1 mouse move, 1 click)

So a grand total of 11 mouse moves, 10 mouse clicks and 13 keys on the kayboard. If max had the ability to read the groups in psd files, and say we could lock the map to look at a specific layer or only at a specific group, the process for saving your file is as follows.

1) Shift-Ctrl-S for "Save As" (3 keys)
3) Hit Ok (1 click)
3) Hit Yes to the "Do you want to replace the old file" dialog (1 mouse move, 1 click)

Which is a grand total of 1 mouse move, 2 mouse clicks and 3 keys, which will save a lot of hand strain, especially when you may do hundreds of saves a day to do test renders of your tweaks.

The Compact Material Editor should have a "go backward to sibling" button. Sometimes the user is working on the diffuse map and decides to check the specular map. If more maps are applied on the material, it requires a few clicks on the "go forward to sibling" button until all the maps have cycled and the diffuse map is back again. Sometimes an extra click is made and the whole run needs to happen all over again. The other route: go to Parent and look for the diffuse map/get back into the diffuse map takes extra time, since most of the times the material preview will have to be recalculated.
Compact Material Editor navigation reminds me of those really old R/C cars with one single button: the car moves forward and the only available maneuver is backward AND left turn simultaneously :)