Like right now. Just one week after the system was announced. It's amazing work by Sony. Many consider the PS3 Slim a poorly kept secret like the PSP Go, but at the end of the day, we only had a few bits and bobs of rumour to catch onto. Sony must have had these things hidden away somewhere. It's amazing they didn't leak.
Anyway, Americans, if you want a Slim, you might want to call up your local stores now. They're in stock. No word on Europe yet, looks like we're going to have to wait until September 1st.