I guess I can add my thoughts on Panther to the mix. I installed Panther on three machines friday night, an iBook 500, iBook 600, and G4 466MHz. I will be installing it on my Dual 2GHz G5 tonight.
First thing I noticed is how slow the install was. Each machine took around 2 hours. I'm betting the G5 install will be slightly faster
But after the install, everything does seems speedier, especially finder operations. Speaking of the finder, I like the new finder windows. I find them much easier to and fast to navigate.
I like the new threaded view in Mail, really cleans thign up.
Exposé rocks! Other than playing around with it, I have used it a few times to clear the way for the desktop. I don't think I'll use it that much to switch applications, as that is what the dock and command tab is for.
Font book is very helpful. It nice to have the ability to disable all those foreign language fonts, without having to worry about messing something up if I went around deleting the ones I didn't want. Having those fonts disabled speeds up font menus and such.
The open and save dialog boxes are new. They are eariser to navigate for the most part, but doesn't allow you to move backwards all the way through the disk heirarchy. By this, I mean if you start at you home folder (possibly by using the shortcuts on the left), you can only go that far back. You have to click on the hard drive shortcut if you want to navigate everything.
Goiodbye DropStuff. NOw Apple allows you to compress (archive) files and folders directly in the finder using gzip format.
PDFs. I can now navigate PDFs on my iBook 500 MHz with Panther, as fast, or maybe even faster than I could using Jaguar on my Dual 2GHz G5!!! Preview is now super fast! Also, the bility to copy text is awesome! I view approximately 3-10 different PDFs every day, on average, so this is a reason to upgrade in and of itself.
Some things I don't like:
The blue box that is drawn around a highlighted icon. I always hated that in IE, and hate it here too. I can't find a way to turn it off.
The Process Viewer and CPU monitor have been combined into the Activity viewer. While the application itself is nice, it doen't allow a nice way to keep a CPU monitor visible. I always kept the little floating bar in the lower left hand corner open, with high transparency, so it doesn't interfere with anything. With this new application, this is not possible.