As I use Linux full-time, I from time to time notice little details that I haven't seen in other operating systems, such as Windows or OS X. I'll post them as I find them. Of course Linux is a general thing, in particular I'm using GNOME 2.20 on Ubuntu 7.10.
Something I noticed today in the file manager (Nautilus): files that are in fact archives (zip files, gzip files, tar files) but do not have a typical archive extension (.zip, .gz, .tar) still appear as archives in Nautilus. Handy. Just noticed this with a ".ywl" file (YAWL). Apparently Nautilus does some file inspection when it is not sure of the file type. Thumbnails of PDF documents can also be handy sometimes (although OS X beats this with its quicklook feature, to quickly view certain document types).