What has changed Finder list view in Lion to make "Calculate all sizes" exponentially faster?
Before Lion, the File Size column in Finder.app would display the size each file requires on the hard disk, not the exact file size. For example, 1 byte files were displayed as 4 KB because they do in fact take up 4 KB of space on a HFS-formatted system. There was no easy way to see the actual file size of 1 byte, other than opening File › Get Info (or using a different app, like Terminal.app and then using ls -lsa, or a Finder.app replacement like TotalFinder.app).

(Back in the day, I reported this as bug 8926275 on bugreport.apple.com.)

As of Lion, this behavior has been corrected, and the File Size column will now show the exact file size for each file rather than the size it allocates on the hard disk (which depends on the file system anyway).

Since these sizes are the same numbers you’d get from the ls binary in Terminal, they’re much more efficient to calculate.