AutoCAD Civil 3D
I never recommend an immediate upgrade, unless you are masochistic, like wfb... 
But it can depend a lot on the size/extent of your projects, as well as the size of your company, and how many other tools you utilize in addition to C3D, and on how many other companies you work and share data with on a close basis. So there's no hard-and-fast answer.
I typically jump to the latest version early for Sincpac-C3D testing. But we typically wait until winter (or when work is the slowest) to roll out the latest release of C3D at Edward-James Surveying. That gives the masochists (like Bill) time to fight all the major bugs, and we usually have SP1 available by then. This past two years have been a bit of an exception, though... We were really busy all through winter 2010-2011, then had a slow-down in June (very bizarre for Colorado). So I ended up rolling out 2011 last summer, because I was too busy during the winter. 2011 proved to be a very bad release (IMHO), so I've now rolled out 2012, even though we're very busy again - 2012 is so much better than 2011 that it was worth taking time out to get it deployed.
Haven't yet been able to determine how good a release 2013 is. But as a general rule, I would not be in a hurry to roll it out prematurely, ESPECIALLY with the DWG format change, and the yearly incompatibility, at least if you often work with other companies. Nothing worse than trying to work with a company that hasn't yet upgraded... Even worse, if you force them to move up to 2013 to stay compatible with you, and then things come back to bite both of you, YOU'RE the one who looks bad.
I know it's difficult to test a new release without rolling it out company-wide... After all, in these days, who has time to waste, recreating existing projects in the latest release of C3D? But it's definitely the safest course, at least if you intend on switching to C3D 2013 in the next few weeks (before there's time for community feedback from the masochists). If you wait at least a month before rolling it out company-wide, you at least stand a good chance of finding solutions to major problems in the newsgroups/forums. If you roll it out right now, then GOOD LUCK....
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