any idea of what improvements?
The major changes the R3 has over the R2 are:
- Sandybridge based dual core processors (i5 - 1.4GHz turbo to 2.3GHz, i7 1.5GHz turbo to 2.6GHz).
- Nvidia GT540m 1GB (i5) or 2GB (i7)
- Inclusion of USB3.0 (1 port)
In general it also has better battery life than the R2 thanks to the SB processor and is quicker "out of the box".
The line is blurred a little once you start overclocking the R2. With a high enough FSB overclock and by using throttlestop the R2 (i5 or i7 versions only) can basically match the R3 for pure CPU performance. A quick GPU overclock can also bring the 335m up to the same level as the 540m.
There are also reports that the R3 is suffering from thottling (processor) and issues of the fan running at high speed randomly.
Overall the R3 is an improvement over the stock R2 (especially the one that is still for sale) but is not really any faster once you start playing around with the system properly. The 540m isn't really much quicker than the 335m either so in GPU limited scenarios there is barely anything in it.
Please note the R2 that was being sold up until very recently (and may still be being sold) comes with either the U5400 or i3 330UM processors. Both of these are quite frankly terrible. Neither has Turbo boost and thus do not perform anywhere near their i5/i7 or even overclocked R1 brethren.
I own a tweaked and fettled R1 (soon to be pin modded up to 2GHz) so if you have any specific questions let me know.