Notice the Mac OS version number change in About this Computer
 
Virtual Memory works more smoothy, and is a lot faster than it has in the past.
 
Finder Improvements
Apple made many changes to the finder, but only a few are visible by the average user. One of the most prominent changes is that the programming code has been streamlined a bit, to maximize performance. In addition, a few interface functions have been improved on, forenstance the added support of descending and ascending fine names in the list view.
 
HFS+ Filing System
The Mac OS Extended format is a major upgrade for the mac's aging filing system which came out in 1986. The advantage is that small files take up less space on big hard disks. You can see the difference most on disks over 1GB. Current downside to HFS+ is that almost all existing disk repair utilities will have to be upgraded, you can't read HFS+ formatted disks with any OS earlier than 8.1 and you *need* the Text Encoding Converter library in the system folder to read an HFS+ formatted disk. If you use a version of norton disk doctor or speed disk before 4.0, you might cause serious directory damage to your HFS+ formatted volume.
  Remember these little things that always used to come up in OS 8 because opening
something took too long to process? They come up far less often in 8.1, which is
great news for all the people I know who have gotten tired of looking at them.
It's changes will amaze you, it's features will let you increase hard disk space for files. What is it? Mac OS 8.1 of course and it's here *now*.
Stability-
Although the OS isn't uncrashable from my experiences, unlike others have reported, it is much more stable that before. Under the "ground-breaking" Mac OS 8.0, many users reported the Finder was slower than System 7.x. With every new OS upgrade, Apple makes the Operating System more stable than before, but Mac OS 8.1 has taken the biggest jump so far when compared to a prior Mac OS release in terms of stability
Speed-
As soon as you install 8.1 from 8.0 (without SpeedDoubler 8), you can feel a noticeable speed increase. If you're one of the people who does have SpeedDoubler, get the 8.1 update (via a search at www.versiontracker.com). My Power Mac 6400/180 works more fluidly than ever before. (Mac OS 9.0 will be a *whole lot faster* SD 8.0.1 is not fully compatible with Mac OS 8.1, but SD 8.1 is available and compatible with the new OS.
Even while running the RC5 app in the background at it's maximum setting, Kaleidoscope 1.8.1 on, while connected to the Internet, a 6400/180 (now, a somewhat lower mid-range mac), everything ran quite rapidly.
Compatibility-
Mac OS 8.1 is almost fully backwards compatible with software developed for all prior Mac System Software releases, including System 6. It also supports floppy disks formatted with Windows 95, and the long filenames associated with them, via PC Exchange.
Customizability
Although the Mac OS doesn't have the themes feature promised in the now dead project, Copland, 3rd party customization tools, like Kaleidoscope worked like a charm on all the PowerPC macs we've seen.
Apple Errors In the OS
-certain open transport-related files need minor repairs, dragging them onto ResEdit or getting the Open Transport 1.3.1 <this issue has been fixed>
-some people have had very hard crashes with 8.1, but adding speed doubler 8 seemed to improve overall stability of the OS (odd, but we've seen it)
-playing MP3 files in the background seem to make the system *very* unstable, which I'm not sure is an OS bug or a SoundApp 2.4.3 one.
A Nice Thing to Add
  With 3rd Party Utilities such as
Jerry's Finder 8.1 patch, you
give more RAM to the Finder,
add some more keyboard
shortcuts, change About This
Computer to About This
Macintosh, as well as add other
The Earth About This Computer Picture is changed to changes to the Finder
Think Different with the patch installed. The patch is available at
<www.manual.com>.
What's new?
-Increased Finder Speed
-Improved Application Launch time with VM enabled
-Increased Stability
-More efficient filing system
-Bug Fixes!!
-Bugs :-(
-Compatibility problems with a few apps (this is a normal occurence, and has been happening when Apple moved from system 6 to 7.5, 7.5 to 8 and so on).
