CURRENT DEFAULT WINDOWS KEYBOARD/MOUSE SHORTCUT SETUP:
UPDATED (2013-06-06)

The Cmd key wasn't working on OSX for a while. Now it's working (version 1.4.06)

SPINE MENU ITEMS: (button on the upper left)
New Skeleton (ctrl+N)
Open Project (ctrl+O)
Save (ctrl+S)
Export (ctrl+E)

GENERAL:
Show tooltip without delay (F1)

Undo (ctrl+z)
Redo (shift+ctrl+z, ctrl+y)
Deselect (space, escape, double click)

TOOLS:
Scale (x)
Rotate (c)
Translate (v)
Pose (b)
Toggle last tool (right click)

ROTATE TOOL:
Constrain by 15-degree increments (Hold SHIFT while rotating)

TRANSLATE AND SCALE
Constrain translation or scaling to one axis (drag the green or red handle. You can switch the axis to be relative to Local, Parent, Global values)

KEYING
Key all changed SRTs, slot images, and slot colors. (K)
Key SR or T for current tool. (L)
Key all SRT for selection. (ctrl+L)

VIEWPORT:
Pan (right click drag)
Zoom (mousewheel, ctrl+right click drag up/down)

Box-select multiple items (drag a box in the viewport starting from an empty area. Does not work if you have a bone or image currently selected.)
Add to selection (ctrl+click or ctrl+box-select)

SETUP MODE:
Set Parent (P) - while a bone, slot or image is selected in Setup Mode.

ANIMATE MODE:
Play forward/stop (d)
Play backward/stop (a)
Jump to start (q)
Jump to last key (e)

Next key (w)
Previous key (s)

Next frame (r)
Previous frame (f)
Hold (SHIFT) with (r) or (f) to move 10 frames forward or backward.

Enable/Disable Looping in Playback(ctrl+r)

DOPESHEET:
Pan left-right (right click drag. Doesn't matter if it's on a selection.)
Pan up-down (mousewheel over dopesheet)
Zoom (mousewheel over timeline, that thing with the numbers below the dopesheet)

Select a key (click on a key)
Box-select multiple keys (drag a box in the dopesheet, starting from an empty area)

Delete a key (double click on a key)
Move key or selection (click and drag on key or selection box. The mouse pointer will look like a move cursor)

Hold (SHIFT) to prevent snapping (to the nearest integer frame) when moving or selecting keys.
Hold (CTRL) when clicking on or box-selecting keys to add keys to your current selection. (You can have multiple selection boxes!)
Hold (ALT) while moving keys or selection boxes to also move all keys after it.

Time-strech/Scale a selection of keys (Box select a group of keys. Then drag the left or right edge of selection box. The mouse pointer will look like a horizontal-resize cursor.)

TIMELINE (the thing that looks like a ruler at the bottom of the dopesheet, next to the playback buttons)
Pan (right click drag on timeline)
Zoom (mousewheel over timeline)
Reset panned timeline (click on scrollbar)
Scrub timeline (drag left and right)
Smooth Scrub timeline (shift+click drag)

With playback loop/repeat on:
Scrub timeline with repeat (click drag starting before last frame)
Scrub timeline without repeat (click drag starting after last frame. This is sometimes useful for when you need to select the last frame in a loop. Sometimes just clicking on the last frame works. But sometimes it doesn't. But for this purpose, jump to last key (E) also works.)

WAYS TO SELECT/EXPOSE BONES:
Viewport: Click on the bone representation (the pointy gray thing with the circle on its pivot point, or a crosshair with the circle in the middle. It will turn white if you hover over it.)
Dopesheet: Click on a transform property (rotate, translate, scale) in the dopesheet under the name of the bone you want. (nice for reselecting bones you recently modified)
Dopesheet: Click on any of that bone's keys. (If you don't drag/move the key.)
Tree: Click on the bone name in the tree (this may involve a lot of expanding and scrolling if your skeleton has a good number of bones)

WAYS TO SELECT/EXPOSE IMAGE SLOTS:
(For image swapping or hiding in Animate Mode, or setting the default image in Setup Mode)
Dopesheet: Click on the Slot Image item under the name of the parent bone in the dopesheet. (Only appears if you've previously keyed an image for that slot)
Tree: Click on the image slot name in the tree (you'll probably need to select its parent bone somewhere else to easily find it in the tree, then expand that bone in the tree to expose the image slot)

WAYS TO SELECT/EXPOSE IMAGES UNDER SLOTS:
Viewport: Click on the image in the viewport (only works in Setup Mode. )
Tree: Click on the image name in the tree

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Non-existing/non-working shortcuts:

Snapping

Copy-paste bones with slots and images (The duplicate button works)

SHOW/HIDE VIEWPORT WIDGETS
Show/hide bone representations.
Show/hide bone names
Show/hide images
Show/hide image names

Enable/disable bone selection
Enable/disable image selection

GROUP/MULTI EDITING
Drag multiple selected images into the skeleton.

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I copied this off of the Trello card:

*Key all changed SRTs, slot images, and slot colors. (L)
*Key SR or T for current tool. (k)
*Key all SRT for selection. (ctrl+k)

Switch tool:
*scale (x)
*rotate (c)
*translate (v)
*pose (b)

*Deselect (space, escape)

*Play forward/stop (d, right arrow)
*Play backward/stop (a, left arrow)
*Jump to start (q)
*Jump to last key (e)
*Next key (w, up arrow)
*Previous key (s, down arrow)
*Next frame (r)
*Previous frame (f)

*Toggle repeat (ctrl+r)

*Undo (ctrl+z)
*Redo (shift+ctrl+z, ctrl+y)
*Show tooltip without delay (F1)

Are these all the current keys? Were there any more hotkeys added since then?
Let's just go ahead and stick (P) in that list though:

*Press (P) to Set Parent for an image or slot, guys and girls.

Also, two really useful keys— next and previous frame— aren't functioning for me.
Can anyone try pressing (r) and (f) in Animate Mode to see if it works or not?

The arrow keys also aren't working. But as they might be relegated to translate nudge, I'm of the opinion that it's fine that those aren't doing as listed.