It would be nice to have "Strikethrough" formatting for text (a button next to Bold, Italics, & Underline). Depending on the client, there are times when we make deletions to General Notes (in addenda) by striking out the text instead of just deleting it.
While I don't think that we'd actually use this feature right now (our General Notes is done in AutoCAD and linked in), I'm sure there will be a point in Revit's future when the Text is good enough to use for GNs, such as by implementing this:
http://forums.autodesk.com/t5/revit-ideas/roman-numeral-list-type-hanging-indent-and-custom-tab-stop...
BTW, this wish is a restatement of http://forums.autodesk.com/t5/revit-ideas/text-formatting/idi-p/6507672