I have used lilypond for the actual compositional process.
It's a royal pain in the donkey, but I'm not sure if I'll work THAT much faster with Finale(Sibelius being way too expensive).
For me Lilypond does work fine for small scores in a "well setup environment".
Well setup enviorment being a window with the code and one with the pdf.
when I press F5 lilypond compiles everything refreshes the score and F6 plays the midi.
Also, syntax highlighting, autocompletion, shortcuts for halving, doubling dotting note values, transposing, etc...
So I just sort of use my money for food and clothing for now and plow trough thousands of lines of lilypond notes.
(don't hesitate to tell me to go buy a copy of Sibelius : P)
Although Gardener does have a point, I might need to try to just write on paper more often, especially for larger works.
(imagine this, a symphony in lilypond, and I want to add an extra bar to some section, have fun making sure each voice that is not used has a rest added at the right spot...)
-Bob