Perfect! Just how a mac app should be!!
Integrates nicely with the browser. It seems to uses the cached file from safari, which makes it so much quicker than the other flash download tools like Tubestock which want to download the video again. It also is not limited to youtube it works on google video (confirmed) and other flash video sites? (according to the limited information thus far in the installer) Although I couldn't get it to work on AtomFilms (maybe the dev can look at this)
It is really quick at encoding the .flv into .mp4 and drops the file into your ~/Movies folder which is fine. A preference for a different location would be nice.
It then does something strange and opens up iTunes? Strange because it doesn't add the video to the iTunes Library? Personally I would prefer to not have the video added to my iTunes lib, but Im sure many would so again a preference setting would be nice.
All in all it is very simple to use and looks mac pretty to boot.
As a app that is in beta this looks very promising. Im now off to Pre-order this sexy little app.

Version 0.88(779) works great for me best version to date. It app just keeps getting quicker. Until now...

Version 0.90(800) cause a kernel panic on the main mac at boot. If the machine actually gets to the startup screen all graphics are completely heterogeneous and I am unable to do anything other than a hard reset.

Started in safe boot, removed .kext and restarted fine. I've since installed 0.88 again and all is working.

Mac mini : Intel Core Duo 1.66 GHz : 2 GB ram : OS X 10.4.9 : Gigabit ethernet