Jason Fried at Signal vs. Noise - Design Decision: Welcome Tab vs. Primer:

"The Welcome Tab in Backpack provides even more information than the old Primer, but it doesn’t get in your way. You can keep the tab around for reference as long as you’d like without it cluttering up your pages or pushing down your content. And when you’re ready you can hide the tab permanently if you’d like.

[...] We think this is a great solution to a common scenario—getting people started but keeping the “getting started” info around for later."

Make sure to read the comments as well.