Can you get SL "Today" folder behavior in Lion?
Phew! I decided to do more digging on my own.

I took a look at a computer still using Snow Leopard and right-clicked on its "Today" folder to reveal its path:
/System/Library/CoreServices/Finder.app/Contents/Resources/CannedSearches

It turns out this directory still exists in Lion!

So go to Finder, and use the Go To Folder command (cmd-shift-g), and enter that path above. The "canned searches" are all still there. Drag and drop them to your sidebar.

Nirvana.