I use the align palette a lot, and I'm constantly switching the value in the "distribute spacing" field from zero, to a given number, and back again. (I want zero spacing between a photo and its caption box, but then I want a stack of photos to be 1p6 apart; repeat.) I would find a button for zero-space to be a really useful constant in that palette.

GREP styles should be user-saveable, just like find/searches are. Instead of having to open up another file, grab my GREP info out of the paragraph styles, and paste it into a style in my new document, there should be a menu of all my user-saved GREP styles available whenever I edit a paragraph style. (Hat tip to @tinahender and @adamjury for this one.)

When laying out the next edition of a magazine, I would like to be able to replace the title and content of the ever-missing Director's text without removing all of his previous column – keeping his signature by example.
This would allow to keep the text structure without having to rebuild it from a emptied text frame filled with blank placeholder text.

Allow text inset in text frames to be spine aware so that you can choose to mirror the text inset on facing pages.

Larger screens make these harder to read.

It's clear, no?

Is not easy to compose with 'full justify alignement' without this option

For example, I can set a Paragraph Style for headlines, with 95% leading. Then I can change the type size of the headline, without the need to keep re-entering the leading.

Constantly run into problems when trying to package an InDesign file with missing plug-ins. There is a multi-step work-around, but I wish Adobe would make it as simple as it should be to strip out of a document the requirement for unnecessary plugins.

We have support for horizontal lines but why not vertical?

I wish InDesign would allow saving a symbol library like in Illustrator. Also, the 9-slice scaling would add flexibility to the creation of graphics within InDesign

Creates drop word effect to all paragraphs with selected paragraph style. The number of drop lines is user defined, and "window" (space) below the word.
Example:

THIS is the Drop word function, i think
its cool idea to add it to Indesign
and I think that almost Indesign users say
to 10x about it.

It would be great if you could select the same fill/stroke options in InDesign that you can select in Illustrator. I know you can remap spot colors in InDesign easily, but this would be great when working with CMYK colors.

MS-Word allow free design for the footnotes line, like a paragraph design. In Indesign, if we want take caption or designed glyphs for the foontones role - we can't do it.

I have a pretty snazzy computer, yet InDesign seems to take a long time to do things like find and replace or reflowing text. Yes these are processor-intensive tasks, but I've got multi-core processors and most of my processor power is sitting idle while Indesign is unresponsive. Proper multi-core support and 64-bit compatibility would be lovely, please?

Indesign Librarys are good, but to be able to place new items where you want as quark would be great.

Just opposite to adjust only first line, this could help to keep an equal distance of Headlines (usually bigger type) to the following body text (that is adjusted to the grid)

1. Ability to set numbering and numbering style per footnote, rather than per page/section/document.
2. They must comply to Text Wrap.
3. Footnotes in tables.

These are necessary features, especially for long document layouts.