I would like to call for a place to list some little things that surprise you about Lion. There are so many articles and lists of all the new features with information overload, I would rather focus this spot of the site on tiny delights with a note why it makes a difference to you.
Please one topic per answer, this isn't a race to enumerate everything that changed. This isn't the place for massive topics like the implications of FileVault 2 on your entire workflow - just a stroll past some little gems, fun oddities or subtle changes specific to Lion.
Answers must relate to why or how you use the feature - links to official tips and tutorials are great, but the intent is to collect little gems that affect how the system gets used. Expect answers that are not specific to lion or lack a personal use case to be heavily edited or deleted.