What are JDI features?  They're "Just Do It" features: small features that don't take a lot of time to implement or test and seem like an obvious improvement.

Here is a list of the JDI features in Photoshop CS6, by category:

Automation

• Contact Sheet II has been restored as an Automate option
• PDF Presentation and Layer Comps to PDF have been restored as Automate options

Brushes

• Add ability to record brush strokes in actions with "Allow Tool Recording" option
• Brightness/contrast slider for textures when painting
• Brush projection for static tips
• Brush tip cursor reflects brush pose and jitter for round and captured tips
• HUD brush resize and hardness can now change opacity - [Control] + [Option] + click drag up/down with General>Preferences> "Vary Round Brush Hardness based on HUD vertical movement" unchecked
• Increase maximum brush size to 5000px
• Change color dynamics to per stroke instead of per tip (user option for old behavior)

Channels

• Enable Split Channels for documents with single layer (so you can split simple transparency)

Color Picker

• allow clipboard paste into hex field with # in contents (i.e. #aabbcc), or 0x (i.e. 0xAABBCC)
• allow shortcut hex values (i.e. #123)

Eyedropper

• Add ignore adjustment layers options bar item for the eyedropper
• New mode for eyedropper to select layers current and below
• Show the sample size popup for the various eyedropper tools (black point, white point, etc.)

File Formats

• Allow for reading more bit depths in TIFF files
• Give the user choices regarding how they want transparency treated in OpenEXR on file open and save
• Read BIGTIFF format (TIFF files over 4 Gig)
• Read common stereo image pair formats (JPS, MPO, PNS)

GPU

• Increased GPU stability by prequalifying GPUs on the fly before use

Grammar

• Grammar policed throughout app
• Use consistent grammar style in the title of dialog windows (no commands such as "Choose a color:")

Image Resizing

• Auto-select the best resample method based on the type of resize (bicubic-automatic)

Importing

• (Macintosh only) Import images from devices provides ImageKit scanning and camera acquisition support

Layers

• Add bicubic sharper & bicubic smoother options when free transforming layers (menu in options bar)
• Add dither options to Layer Styles for Gradient Overlay and Gradient Stroke
• Allow 00 or Shift 00 to work when setting layer/fill opacity (previously no way to get 0%)
• Allow changing color labels on multiple layers at once
• Allow changing of blend modes for multiple layers at once
• Allow locking of multiple selected layers
• CMD+J to duplicate selected layers and layer groups (in addition to layers)
• Layer tooltips to include layer name (if defined)
• New command to rasterize layer effect into layer, merging the selected layers into themselves (Rasterize Layer Style)
• Opt+click on toggle arrows (groups and effects)in layer panel should close all targets
• Reorder effects in the layers palette to match the Z-order style/blend mode (bottom most effects in terms of blending order, drop shadow is below the other effects)
• Show blend if/Blending Effects badge on layer if they are not default values
• Show correct opacity and blend mode values for hidden layers
• Tab goes to next layer on inline layer rename, SHIFT + TAB goes to previous
• When creating a shape layer, the layer name should not be like "Shape 1" but instead reflect the tool named such as "Rectangle 1"

Liquify

• Add option to load last mesh
• Increase maximum Liquify brush size to 15,000
• Resize Liquify brush with shortcuts: bracket keys [ ] now match same increments in Photoshop
• ctrl (win) / cmd (mac) switches to magnifying glass
• alt + right click + drag to change brush size (win)
• ctrl + alt + left click + drag  to change brush size (mac)

Masks

• Enable Invert and Threshold adjustments for masks in 32-bit/channel

Plugins

• Hold SHIFT during startup to disable Optional and 3rd party plugins

Presets

• Add New Document presets for common devices (e.g. iPhone, iPad, etc.)
• Add new Gradient Map presets for traditional print toning and split-toning
• Sticky reorganization of tool presets (changes persist after relaunch)
• New HDR Pro presets from RC Concepcion and Scott Kelby

Printing

• Add "Edit" button for the description field in the print dialog
• Allow print dialog and print preview window to be resized
• Allow user to change the "preview well" background color in the print dialog
• Allow user to manually position the printed area on the page
• Hide color profiles that are inappropriate for currently selected printer when using "Photoshop Manages Color"
• Reintroduce "Print selected area", allow user to modify selection in print dialog

Save

• Add warning message that 16-bit images cannot display their file size in the Save as JPEG dialog

SDK

• Add ability to access tool name associated with the tool preset name via scripting
• Add the ability to return an array of guides in a document from the scripting SDK

Selections

• Make the marquee, lasso, and mask panel feather values support decimal places like the feather dialog
• Remember feather radius when showing dialog for selection from a path

Transform

• Don't hide smart object icon when transforming a layer
• Improve dragging of vector curves
• Rotate 90 with even x odd pixel dimension to not land on a half pixel position
• Preference to disable auto-rotate on open

Type

• Add command to insert "lorem ipsum" for type
• Added Gamma rendering parameter for better text rendering

UI

• [Windows] New/open document to context click on a document tab (has always been on Mac, now Windows too)
• Add "Don't show again" checkbox to Purge warnings
• Remove the app bar and reduce the drag/app bar over 30%