Upgrading to k2 v2.1 & allvideo3 I found the same problems as I had with k2 v2.0 (stable) & allvideo3.

1. videos still do not follow width size rules set up in the categories (see attached image).
2. when k2 system plugin is enabled it breaks the smoothgallery module by camp26 (unsure whether it's k2 or smoothgallery so also reported this to camp26).
3. when dimming is enabled in allvideo3 it still breaks the tabs on the add/editing item page.