I think that the Data > Thumbnails > Create and Data > Thumbnails > Update functions should be merged into a single function.
If a file doesn’t presently have a thumbnail, create it, move to next file.
If a file does have a thumbnail, update it, move to next file.
I use these two functions so much that I have assigned them keyboard shortcuts in the Mac OS X System Preferences. But it’d be really great if they were one function, not two.