About a week after I got CS4, I suspect. I'm happy enough with what I have, though I wish CartoPGM worked in CS4. I have to start up my old CS to deal with PGMs, which takes about five times as long as starting CS4 'cause it's in emulation. Apparently the internal photoshop import/export plugin for PGM doesn't handle grayscale properly. At least so far as Bryce is concerned.
I figure if CS4 breaks an old plugin CS5 will and probably vice-versa. Annoying, that.