you dont lose your game when u upload it... the profile on arcade is not yet setup.. but if you press upload game, youl find ur projects that u upload in left side of screen, you can also go to profile from there, and see all ur games and stuff, and bookmark that page ur at, so you dont have to always click the upload game button.
its still in beta, cause scirra has not enough time for it i guess.
but i bet the team will finish it soon, plus with the C3 development process, and the things their cooking the arcade section doesn't fall on the important thing list at the moment atleast. but that is just my opinion.