Young hackers who have a surplus of income and have funds to spare that aren't being channeled toward debt / family / donations, heed me: save as much of your salary as you can, and put it in boring investments (index funds / etc), probably through vanguard.com (no affiliation, I just use them and have heard nothing but good things from people I trust). You can pretty easily set up your job's direct-deposit system so that a portion of your salary goes directly into your investments without you ever seeing it, it's a good set-it-and-forget-it system. It adds up over time!
[Somewhat related: http://www.mrmoneymustache.com/2012/01/13/the-shockingly-sim... ]