Do you have examples? I currently have libav on my Debian machines and ffmpeg on my Ubuntu machines, but haven't really noticed a difference for my needs. I'm not doing anything too complex, admittedly.

Same with me, ffmpeg worked accurately and was extensively documented. Then a day there was no more here. I tried to understand the reasons and adopt avconv despite the ego wars, and those irritant message, and the cumbersome new syntax, and the lack of tutorials in internet... but finally the problem is that avconv just did not worked, and nobody really knew what to do with it.

In the end I stopped using both programs. One was aparently unsafe and not installable without breaking things, and the other reinstall itself constantly, acts in a questionable way, and did not solve my problems. I guess that for Debian this was a false step that consumed time and resources but did more damage than good. Libav probably damaged also the image and dominant position of VLC. After several errors and troubles since them, its current luster is not the same as in the first years in my opinion.