The sound issue has been true all along with S3 & TivoHD too, IIRC. It's something along the lines of -- if you're using a digital connection for audio, Tivo can't "overlay" its sounds on top of the regular sounds. I turn the sound effects off immediately so it doesn't bother me.
I have a new Premiere 4, and I too notice a bunch of bugs. (I had one apparently busted Premiere 4 that was hanging/rebooting almost every day, but exchanged it and the new one has been working for a few days with no major problems, knock on wood.)
Bugs I notice (these are all with NON-HD UI):
* You can still PAGE DOWN at the end of the Suggestions list, and maybe other lists.. Basically it doesn't always know when you're at the bottom of a list
* This is one hang I saw on BOTH the 'dud' and the new one. I'm afraid to try it again, but it MAY only happen in the 'initial set up' when it has partial guide data. If I chose "record this episode" (NOT going into the Options) for a specific episode.. IT WOULD HANG. The remote light on the machine would still flash, but at least in one case I left it there MANY minutes and it never recovered. One other time (on the dud one), I did unplug it..
* Going left out of a show/group OFTEN doesn't put you at the right place in the list you were previously. This happens in a few specific instances on my Tivo HD.. But fewer places.
* Getting Now Playing in kmttg is almost instantaneous. (But I haven't actually been able to download a program yet, haven't figured that problem out yet.)
* SOME UI is snappier. A lot of people seem to think it's a million times faster. I think it is, e.g. changing SP list or recording a new episode/setting up SP. But some other things seem as slow/slower.