I just installed the update. Had a screen pop up saying 'update is ready etc' but there was no yes or no buttons, so i went to advanced and clicked 'force update' then clicked on 'reset core/hybrid'. The update itself went really quick, the longest part was waiting for the orbiter screens to regen and render.
My mythTV version is now 0.20.20070821-1.
It solved the major problem i was having with mythtv, namely video quality. Previously tv (dvb-t, Australia, both SD and HD) showed artefacts of poor signal strength, glitches, blocking etc. There was also some distortion around areas that had fast movement, peoples mouths etc. This was evident in both 'live' tv and pre-recorded shows. That is all gone now, it is just as crisp and clear as my tvs built in tuner. I have only played with it for three minutes so i don't know if recording stability has increased (I previously had some trouble with scheduled recording, but i only have the one tuner so i may have been asking too much of it in terms of back to back shows, overlapping etc)