GREP searching was a highly needed and really convenient addition to InDesign, when it was added in CS3. Earlier, doing complicated search/replace, and cleaning up documents for extra spaces, tabs etc. was a longer procedure.
Still GREP's greatest force (in my opinion) inside InDesign was added in CS4, when GREP styles was introduced. Being able to change text appearance based on regexp is amazing.
As always, a little something for the wishlist:
Using groups in GREP styles
Being able to search for a longer string, but only applying the character style to the matched part of the results. If you want to highlight the word "bar", but only when "foo" is in front of it: "foo bar" >< "this bar". I would suggest being able to search for something like "foo (bar)" and only apply the character style to the group, "(bar)".
Character and paragraph style aware GREP searching
Prior to CS3, where GREP was introduced in InDesign, I normally would export the text story as InDesign Tagged Text and apply all my advanced searching on that document in any text editor. And I still do this, because what InDesigns GREP search lacks, are character and paragraph awareness.
In GREP search you are able to find/change formatting as well, which lets you target specific paragraph styles, but you are unable to search for "paragraph_style_1 followed by paragraph_style_2"-combinations, which can be really handy if you want to remove e.g. indentation from all paragraphs located after blank lines, subheadings etc.
Searching on pairs of paragraph styles isn't possible inside InDesign - to do the more advanced searches you still have to export the document as InDesign Tagged Text, and do the searches in your preffered text editor.

Also, you can use the regular regexp anchors, ^ and $, but these only applies to paragraphs. So if you search for a specific character style, you can't tell InDesign to look in the beginning/end of the found text, it only applies to the current paragraph. A set of extra anchors in InDesign please?
Searching from the beginning of a character style doesn't work. The ^ anchor still applies to the beginning of the paragraph.




