I'd have to thank element14, especially doctorcdf for this "mystery date" which turned up on my doorstep unannounced.
I've done some comparisons, benchmarks and high-resolution photographs on my blog here: Valentine’s Day: A Date with the Raspberry Pi 2 (Model B)
In short, the conclusion reads:
It seems the Raspberry Pi foundation aren’t under any illusions as to the reasons behind their success, and the latest Raspberry Pi 2 Model B retains the key points that has driven the Raspberry Pi’s success – namely, the low cost, and straightforward backwards compatibility, which allows for the platform to feel “homogenous” without being hemmed in by the original choice of hardware.
While the benefits of the increased core count will not necessarily be apparent to single thread tasks, the CPU also delivers with a more recent architecture which allows the performance per clock to increase. As a result, it appears the new CPU has much better single thread performance in part due to better caching and memory bandwidth, even comparing a stock Pi 2 to an overclocked Pi. The multi-core advantage makes sense for many tasks, as they may involves running multiple threads – think of certain server tasks with a thread per connection, dynamic content generation invoking multiple tasks, using one Raspberry Pi to do multiple things (e.g. attaching several RTL-SDRs), handling data and display on the same unit or handling multiple sensors.
It’s amazing that they’ve been able to work closely with Broadcom to specially produce the BCM2836 for the Pi 2, no doubt in part due to the major sales volumes generated. Through their refinement, they have been able to keep the cost identical, while offering so much more. In everyday use, the difference is very noticeable, from boot times through to actually using the device. It is much more pleasurable to use interactively, with less patience required compared to before.
Of course, being the natural evolution of the Raspberry Pi, it is expected that most purchases from now-on will be of the Raspberry Pi 2. Is there any downside? Well, the only one I can see is in power consumption under load and incompatibility with non-upgraded distributions (not so much an issue for Raspbian based OSes) – but aside from that, it’s pretty much a free lunch!