I find equation entry on lyx rather nice (being a long-time latex user), but editing leaves something to be desired. I find it almost impossible to mark, cut and paste parts of equations. Almost every time I try, I wind up selecting the whole equation and starting over.
I hope this can be improved. I wonder if any synergy with kformula could be found? I haven't used kformula a lot, but from my limited experience it seems really nice (except that it doesn't seem to allow latex-style entry).