I came across a rather interesting post today on the various newsgroups on the web, it was a discussion in changing the length of time in which a notification banner persists within the left hand side of the screen. These are the ones that appear when your get a new mail message, iTunes track, or a variety of other messages. With a nifty terminal trick you can change the length of time in which this message is displayed.

Full article here:
Adjust The Notification Centre Banner Time (MacTricksAndTips.com)
Related:
Best OS X Mavericks tips and tricks (TrustedReviews)