General todo items
- Pressing number keys when changing brush size not back from 2.4x #28811.
- Add option to allow xray and ztransp work together. This is a know limitation of Blender, you can see the problem if you have a Material with alpha and Transparent display enabled, turning on X-Ray has no effect (more information in the tracker, #21987)
- Change the make_links (editors/object/object_relations.c) operator to show a menu with the properties that we can copy for every object type. Also finish to port the rest of options from 2.4x to 2.5 (like Camera data).
- GLSL drawing doesn't support custom clipping.  and #26363.
- Copy/paste into Text Object edit mode
- Textured draw defaults to single-sided for non-textured objects. Not very useful for a 3d editor...
- Continuous grab doesn't function when switching view3D modal. See #28486.
- Numpad orientation is not aware of rotate around selection. See #31605.
- Helper objects (empties, force fields, lattices, etc) are not scaling to grid cell size on add. #32219
- Image Sequence & Movie texture is not being updated on frame advance (using textured solid and multitexture textured shading modes, in 3d window). GLSL materials do update.
- Some Game Engine settings (like transparency) draw in viewport, also when render engine is not "Game".#31294
- Lattice drawing colors are not part of Theme Colors yet. #35575
- Image pinning state button in header.
- Lock image.
- Image drawing is using glDrawPixels, making it only support unfiltered zooms. A switch to texture drawing would cause slowdowns though... should be compensated by switching to GPU operations for all drawing and painting options. And solve handling huge images (8k or more).
- While painting in sequences or movies, and having same sequence update live in compositor, black frames can appear. This is because images get moved to linear color inside composite, and paint system is accessing the same data. Both color management and image buffer 'owning' needs better handling.
- N/T shortcut keys for panels are inconsistent in that they have left/right switched compared to 3d view. (report)
- Image repeat is currently limited by 0.25 sec, need betterapproach drawing tiles here (report)
- Image editor in UV edit mode does not do real face tessellation which ends up with some artifacts for concave faces. See #31074.
- Find out how UV/Image editor should track other editors or the active object when setting images or uv maps. See #33055.
- Improve feedback on unsaved painting when saving .blend. See #34235
- Put back feature to allow scrubbing on individual strips (but consider usablity), see #27712
- Animated properties currently don't work on single-image strips without blend mode, see #21378
- Strip blend mode "replace" doesn't allow animation
- Scene strip preview drawing prevents RMB insert-key on buttons. Use autokey, disable preview, or use graph editor for now. (This is a todo after 2.5)
- One solution is to implement "animation overrides" as detailed in this, see #25020
- Preview image / scopes have no view navigation (zooming, scrolling).
- Improve/replace current plugin architecture, see #22579
- Add a check to the preview renderer to detect whether graphics cards support off-screen render, so that people whose graphic cards can't handle those textures get better feedback. See #24656 and #22081
- Sound strip volume is only evaluated once per frame, so animating the volume leads to audible volume artifacts, see #24194
- Built-in replace/alpha/etc effects only work when there's a strip below. Could work for single strip too.
- Changing the pitch of a clip does not really change the pitch but changes the speed, see #28533
- Video dimensions aren't detecting correct for some codecs (leading to black "outline" on the bottom or right of shot). See in comments for #26837
- Movie strips aren't getting cache-limited which leads to high memory usage by internal anim structure fields.
- Cache invalidation doesn't happen reliably due to lack of dependency graph, #32206
- 10bit movie files are internally reading as 8bit byte, #34755
- Global undo doesn't work with editing text. (also mentioned in Interface category) link
- Old todo: text files are default included in .blend files, no support for external text works, nor does it support relative paths 
- Tab width is just a display option and it's not effect on indentation. See here.
- Datablocks view
- Does not remember state yet after save/load.
- Needs a system for viewing e.g. a million vertices, right now can run out of memory.
- Button drawing style would be nice to have as it was before without border.
- Calculation of width of data in columns needs revision. Currently uses hardcoded width hack
- RMB menu items should be reviewed (see here)
- Recursive toggling hide / hide_select / hide_render is possible by holding Ctrl, but there is no way to keyframe all children recursively (should be Ctrl + I).
- add the ability to run a command in another context (using the mouse, text dnd)
- add utf8 support #30777
- Add support for FILE_OT_directory when used with linking or appending to type in names that include blend paths and proceeding ID groups such as /tmp/foo.blend/Scene/
- More expectable default folder for file selector #31314
- Bookmarks are allowed to be added when browsing inside a .blend file, however - this can't be used.
- Horizontal layout doesn't trigger properly correct sliders when panels are larger than what fits in area (see also this report).
- Have some way to specify which AnimData block Action Editor's action field gets/sets from
- Multi-Dimensional arrays such as UV's or Matrices don't have access through animation path creation and lookup functions.
Editing F-Curve keyframes through the right hand panel's number buttons doesn't recalculate the curve, see report and report and report
Selection syncing for bones and fcurves, see report
- The names of sub-structures are not shown in a very useful way in the dope-sheet, see: http://projects.blender.org/tracker/index.php?func=detail&aid=33178&group_id=9&atid=498
- Allow separate RGB + A channels in Output File and Image nodes (Image + Alpha sockets), for the same RGBA file/layer. See report