One of my Mac OS pet peeves from way, way back is how the Finder handles a double-click to a file in the Trash. Sure, I know that opening the file may prevent me from effectively emptying the Trash, but I really would love to know what's in that graphic I tossed weeks ago before I wantonly delete it. Wouldn't it make more sense to open a temporary version of the file, or have that dialog offer to move the file back to my Desktop for me? C'mon, Apple, throw me a bone here.
Much to my glee and moderate surprise, Quick Look works like a charm on files that are trashed; that's exactly what I need to check that the files I'm throwing out are actually what they purport to be (not that I'd throw out the TUAW logo, that's just an example of a file I need to rescue). The more time I spend with Leopard, the more I'm convinced that Quick Look, as humble and subtle as it is, may actually be the killer feature of 10.5.