M.M.
My son is also 19 months now. He went through a hitting phase (luckily it's over now I think...*prays silently*)
He is generally well behaved but IS very "hands on." He touches EVERYTHING, and is mastering climbing on, in, under, over EVERYTHING...
I've told him no, but he doesn't care. I've made stern faces, he doesn't care. We've instituted "time outs" in the naughty chair and while it hasn't been magical...it at least helps us distinguish limits. I'm totally ok with his touching stuff...so long as he knows that when Mommy says NO, she MEANS NO! Now is the time to establish discipline as he's reaching a dangerous place...lol...since he can REACH just about everything!!!
My son doesn't seem to MIND time outs so much. He sits there happily for up to 2 minutes...and enjoys a hug when he's done. I've even found him putting the chair in the naughty spot and hopping in when he's not in trouble... So I wonder how deeply effective it is at the moment, but it DOES give me as the parent an option of really establishing, that whatever just happened is not ok.