The largest I know of is my editor, I haven’t had too much performance issues (besides precompilation and starting time) but I don’t have much interaction between the widgets, it’s mainly “press a key => do something” type of things. That said the windows version doesn’t really work (because of Gtk.jl issues afaik).
I guess being able to statically compile our applications would be ideal, but that will probably require some rewrite of Gtk.jl and a lot of work (see Compiling and building binaries from your julia code - #47 by sdanisch).