My company has, in the past, tended to stay 1 release behind current, to give time for all the bugs to be worked out. We were on 2011 until about this past September, when we just jumped straight to 2013 and skipped 2012 entirely. The improvements we've seen coming for 2014 suggest that our Nat'l CAD Mgr is going to jump us to 2014 the second it hits the streets, because it looks like some things that he purely hates about <2013 are going to get changed. After that, I suspect we'll be sticking with 2014 for 2 years, to get back on the 1 behind routine.
As for hardware, when we buy workstations we get an extended warrantee, and usually keep the workstations until they're out of their (generally 4 year) warrantee, then upgrade. There are exceptions to this rule, however: the other guys in my office somehow wound up with first-gen I3's for Inventor workstations, and this didn't work out so well. They complained - justifiably - until management bought them better machines. (I already had the good computer, fortunately ... my old workstation, a C2Q 6600, had gone off warrantee right when the company realized that i3's weren't really cutting it for Inventor.)