I've been trying out MuseScore this past week, and although I hate to admit it I'm afraid it may be winning me over from LilyPond.
When I tried MuseScore previously, I was entering notes the stupid way with the mouse and didn't like it at all. Now that I understand the keyboard controls, it's very easy. I still really like the concept of LilyPond, and as a programmer I like the idea of plain text source files (I have a lot more faith that I'll still be able to open a text file in thirty years than that I'll be able to use some binary file format), but entering notes into MuseScore is just easier. My LilyPond editing sessions always involve a lot of back and forth as I compile, look at the pdf, and realize that I've gotten my relative pitch off track and need to move some notes to the correct octave.
I might still prefer LilyPond's output. MuseScore can export to LilyPond files, but those files still need some tweaking. The exported files are particularly clean for program-generated source files, however -- much cleaner than, say, program-generated HTML -- so I don't mind working with them. I think my new workflow is going to become, 1) Enter notes into MuseScore, 2) Export to LilyPond, 3) Tweak until I like the printed output. Time will tell how optional steps 2 and 3 may be.
Thanks to flameproof and our other MuseScore users for touting its benefits enough to make me give it a second look.
Edit: On the other hand, MuseScore does like to crash a lot. Does that happen to anyone else?