The span between Q4 and Q3 being a quarter and not a year.
As a side note it will be interesting to see if this improves performance on Sandy Bridge hardware.
For 3D performance, you should expect around +40-60% FPS improvements in 3D games. Of course, your mileage may vary from game to game, so you could check Michael's benchmarks for more precise results.
For 2D performance, with latest Cairo development version, it is possible to expect around +20% performance improvements for most workloads (but it changes dramatically between different test cases, from 10x performance increase in some cases and down to 10% performance regressions in some corner cases, most notably ones being firefox ones. However, for those, this difference is around statistical error, as those workloads are quite fast anyway. So 10% performance decrease corresponds to increase from 2.59 to 2.9s in cairo-perf benchmark).
I hope it clarifies things a bit.
Of course, all the usual considerations about benchmarks apply - I've just given an approximate summary of what I am seeing on my machines .
I only know how to update Linux Kernels with ppa's but the packages provided on the site leave me in the dark.
What the site is saying is that "These versions here have the improvements we're talking about"--it isn't a special package you need to get there, it's links to the upstream source code.
Look up the versions listed on Launchpad, and see if they are available from a PPA.
Otherwise, you can compile from source.