Make a backup of at least your user folder, if not a clone of your main disk. That said, install with confidence - this is not windows yet
Some 3rd party stuff will work if it doesn't involve icon haxies, or a hack on the graphics. Things that do not work will not hose the system - perhaps a dialog or 2.
Install takes around 30 minutes on newer machines (even if it starts with a 2hour+ time count)
Some welcome new features in email and ical.
Cover Flow might be useful at certain times, but slower than list view when you need to get things done. It is an interesting option though. Quick View is nifty.
If you don't want to use 2 clicks for a dock folder to open as a finder window - use command click. A preference would be nice. The doc folder grid is impressive, but many users will prefer a list view in folders that have many items.
The translucent menu bar looks to be around 30% or 70% depending on how you calculate the see through. I'm neutral on this effect, but it may bury some dim icons with a grey desktop color. Brighter colors tend to have a better effect.
Translucent menu backgrounds are another matter. Bookmark text on a dark browser window tends to loose it's readability.
So far, I see a speed boost on Apple's native apps, and a hit on the GPU. MacPro users with high power cards will probably see a boost in the GPU. Older Power Books and iMacs might draw a little slower. All this eye candy comes with a price. Now I know why there's an 800mhz floor on Leo. He's hungry!
Quicktime seems to handle wmv files better - thank you.
Once you get past the huge amount of `Bling' in this release, you'll find some very useful improvements. Time Machine could take away 3rd party backup utilities once it matures. It will no doubt sell some fire drives right away.
Have Fun!
