Initially the Raspberry pi was launched as a ARM 11 running at 700MHz. This is equivalent to an old Intel Pentium 3 processor.
Compared to other boards like the BeagleBoard that have a ARM Cortex A8 core and a DSP processor, it is a low performance board.
The first improvement in the global performances was with the announcement of the recompilation of the packages of the raspbian distribution with hardware floating point support.
This is not an hardware performance improvement, but it is an improvement on the use of the hardware. The gain was visible in the applications that uses intensively the floating point arithmetics, for example the graphics.
Then the hardware improvement
A few day ago they announced an update on the firmware that allows to run the raspberry pi at 1GHz without loosing the guaranty or reducing the lifetime.
The gain is up to 52% faster on integer, 64% faster on floating point and 55% faster on memory.
So a widely used and intensively supported product like the raspberry pi can give good surprises after the launch, like the distribution that have evolved, the performances, etc.
This for free without changing your board!
So what we can expect for the next improvement?
Maybe the support of GPU acceleration with OpenCL? Hum, the GPU firmware is very closed, and the manufacturer seems to don’t be ready for OpenCL. But the amount of user may put some pressure on them.
A new version of the distribution recompiled with support of the SIMD to improve the global performances? I don’t know if this can increase the performances, but for sure the power consumption.