The first HSPA+ dual carrier smartphones are on the market now and I can already imagine of how they will be marketed: It can do 42 MBit/s! That's easy for the press but it completely misses the point.
It's not the theoretical top speed that will make these phones better for users than their current models but their ability two bundle two 5 MHz carriers. While this allows for the theoretical 42 MBit/s top speed, the real sweet thing about this is that it also doubles cell edge performance. Here, the signal strength is low, interference is high and as a consequence, data rates are much lower than closer to the cell tower. Having the ability to bundle two channels in effect doubles the data rate in many places with a weak signal and high interference and that will be noticeable to users.
Another benefit not to be underestimated: Dual-carrier chips usually come with sophisticated interference cancellation technologies and perhaps even two antennas for diversity. This again will do wonders in areas where the neighbor cells and even data sent to other users from the local cell creates interference.
Networks will be happy about such devices, too as the 64-QAM modulation and interference cancellation technologies will implicitly increase overall network capacity as data can be sent to such mobiles in much less time than to non HSPA+ devices. In other words, more time is left to communicate with other devices.
Let's see if the main stream press will take note of this at some point.