Roll back a year. Linux had two versions with difference performance. The Ubuntu desktop edition used standard Linux and featured some changes to make startup faster but did nothing for regular processing. The Ubuntu Studio edition added special modifications to reduce latency when using real time software.
Real time software includes recording audio and video live plus processing the audio and video while recording. The slightest latency creates an error between the signal and the editing. Ubuntu studio contains a selection of changes to reduce those latency inconsistencies.
Lunux 2.6.38 includes some changes to reduce internal delays. The changes will help Ubuntu Studio. I do not know when Linux will finally adopt all the latency changes included in Ubuntu Studio but this appears to be one step forward.
My Ubuntu 10.10 computers recently upgraded themselves to Linux 2.6.35 and performance improved, most noticeably in Thunderbird. 2.6.38 looks like producing a similar step up in performance.
Linux 2.6.38 has some other improvements. None that will produce significant changes for regular use. One of the performance improvements will be visible only in large applications but the change can help smaller applications when they are rewritten to make use of the change. One change will be noticeable only for multiple core processors and almost all new computers have been multicore for a couple of years.
We are seeing Linux catch up with Windows in the few areas where Linux is slower than Windows. At this rate, within a year or so, there should be no areas where windows can beat Linux. If you are buying your next computer this year, try Ubuntu Linux on your new computer. You should see some improvements and no disadvantages.