I had been running 10.0.4 for about a week on a 500mhz TiBook w/ 384MB of RAM.. Here's my impressions...
First, and most importantly, the Finder is slightly accelerated. Window resizing is still sluggish, but if you have a folder with lots of files in list view, scrolling through the list is much faster than 10.0.3. Application launch times are about the same, maybe a wee bit faster. Nothing major though.
DVD playback wasn't present in this build, but there was a seperate file with DVD playback that I couldn't get to install. It was about 4MB in size. Also missing was any Disc burning capability for data.
Among the files updated were the graphics drivers for just about all the supported cards, including the new nVidia GeForce 3.
In my testing I uncovered some serious bugs. Most noticeably was a bug that whenever you would log out, the system would hang in between presenting the log in screen. A reboot was needed.
Also, the Installer application would crash anytime you tried to authenticate by typing in your password.
The build (4Q4) was dated May 30th, so I'm sure it's been updated since then.
10.0.4 will probably be released in tandem with OS 9.2, since 9.2's fixes mostly benefit it when being run as Classic. When is anyone's guess. go2Mac is saying as early as today. My guess is that SJ will hold it until next week during the NECC conference.
I finally reinstalled 10.0.3 over this build because the login/logout bug was just too much of pain to deal with. Of course, I'm sure this will be fixed when it finally gets released... Whenever that may be....