To answer that question I always ask myself, "How will this upgrade affect my daily use of the Mac?" I primarily use my Mac for email, Internet, iApps, Office v.X, Photoshop and Dreamweaver. Pretty basic stuff.
I use Expose daily and it has made my life so much easier. No more minimizing and rearranging of windows, just one click and - BOOM - instant desktop. The combination of Fire Vault and Fast User Switching has finally convinced me to set up accounts for family members and it's been working out beautifully. The updated Finder not only makes the Mac more customized (for each user no less), but has made finding and saving files a breeze. The ability to print address labels and mailing lists from Address Book is a much welcomed addition that I will be using frequently. Having drag and drop email addresses and the sorting of messages by thread added to Mail has greatly improved its use. I couldn't be happier that iChat AV is included, as it's become an integral part of my keeping in touch with friends and family across the nation. The Mac turns on faster and everything (especially Finder, Help and Safari) runs much faster than in Jaguar.
As others have noted, installation is very easy and usually painless. My installation went off without a hitch and took about 45 minutes total. However, I have run into two minor problems since installation. My Visor PDA no longer syncs (I understand this has to do with the Hot Sync application not being updated for Panther) and I really can't stand that brushed metal look of the finder (luckily I found shareware (whiteout) that takes care of that).
So how has the Panther upgrade affected the daily use of my Mac? Panther has boosted my performance, given me enhancements that I now can't live without and somehow, I enjoy my Mac even more than before. I didn't think that was possible. Leave it to Apple to deliver the impossible.
It is a clear (even if incremental) improvement from OS 10.2, and at least one friend who is a Mac user told me that an upgrade to OS 10.3 from OS 10.2 eliminated what had been an annoying software conflict. But I think that anyone who is comfortable with OS 10.2 might be better off sticking with what they have and waiting for OS 10.4 or 10.5 before making the leap.
But for users still using OS10.1 or something older, I think this would be a great investment, adding stability (when I used it OS 10.1's stability was undermined by a lot of bugs that were worked out in the following generations), slick new features like Esposé, and an interface that's easy on the eyes and more intuitive than previous versions.
I've been using 10.3 for about three weeks, and I am very pleased. Prior to installation, I experienced frequent crashes, sometimes several a day. Now they are very rare (two in the last three weeks). I find that the Safari browser is faster and more reliable than Internet Explorer. Sometimes IE gets hung up on displaying a web page. I switch to Safari, and the page comes up in a snap.
The new version of Sherlock is very slick, but I can't figure out how to do something that was very simple with the older Sherlock 2, namely locate a file on my hard drive. There must be a way to do it in the new Sherlock, but it's not obvious. The online Help was of no help in figuring this out. So I just use the old Sherlock 2 in "Classic" mode when I need to locate a file on my hard drive.
Certain features that had ceased to work with 9.2 now work just fine with 10.3. For example, before installing 10.3, I couldn't get my CD ROM to recognize and play music CD's. Now, through iTunes, it works just fine.
One complaint: Apple recommends that you install the latest version of OS 9 for "Classic" mode. I had 9.1, but the latest version is 9.2. I had to pay $20 for this upgrade. I think this upgrade should be included with OS 10.3.
Overall, I'm quite happy with my new Panther.
