I don't know about Excel 2007, but the current and previous versions do not have an efficient text editor for entering complex formulae into spreadsheet cells.

You can use alt-enter for line breaks and spaces to indent, and Excel color codes cell references and parentheses, but each line break and space counts against the maximum formula length limit of 1024 characters.

Entering nested conditional formulae quickly becomes confusing, and editing someone else's work can be very difficult. A code editor that recognizes Excel formula syntax, handles indenting of nested functions, color codes things better than Excel's formula bar, and allows comments would be very handy, especially to keep formulae concise. It should count characters (but not line breaks and indents) and enable single-click to copy all to Excel sans breaks and indents and comments. One could save the formula code with comments to a text file for later use.

I've heard Excel 2007 eliminates the formula length limit and nested function level limit. Unless Microsoft is already building a text editor into Excel for formula entry, a jEdit plugin for this will become a very popular tool I think.