We just got our 2.5GHz Penryn / 4GB fourth-gen MacBook Pro. Plenty of power under that hood, but the outward differences are few: it's got the new, reorganized F-key layout (which we're not all that fond of), and the trackpad physically the same (with the addition of multi-touch, which works just as well as it did on the MacBook Air). It's definitely an anticipated upgrade to the flagship, but whether you think the form factor's still got the longevity necessary to keep you coming back after, what, more than two years on the market with no major changes -- well, we'll leave that to you. We'll have some updated benchmarks shortly.
P.S. -It includes the same model 60Wh battery they've been selling on these for a while, for those puzzled about the battery life changes made to the Apple's MBP spec page.
AppleMacBook Pro 15-inch with Retina Display (mid 2014)