In the most recent Safari update, 5.1.1, the Show Downloads menu item is back with its original shortcut, Command+Option+L. The only strange behavior is that it will be unavailable if your download history is empty (and of course that it is stuck to the Safari window). Otherwise it works like in Snow Leopard.
Thanks unnamed Apple hero!
[crarko adds: I guess I didn't notice it was missing, but it's good to have it back. Now Apple heroes, let's please have that modest iCloud support for Snow Leopard. :) ]