For the ump-teenth time, I've been asked "how long does the new graphic persist on a new document or list item"?
Well, according to this guy the answers are:
"How long does the New! icon display after I add an item?" and "How do I prevent the New! icon from displaying?"
The New! icon displays for 2 days by default, but you can use the command line to set that:
[SharePoint Bin Directory]\stsadm.exe -o setproperty -propertyname days-to-show-new-icon -propertyvalue [Days to Display] -url [Your Virtual Server's URL]
To hide the New! icon, set [Days to Display] to 0. An alternate and unsupported approach is to replace the New! icon with a clear gif file.
The only problem with this answer is that it always takes me 10 minutes of searching to find it. But, I just fixed that problem by posting here... :-)