Graphics primitives under Tiger are a lot faster than in Panther. For example, Tiger draws lines ten times faster than Panther's Quartz, and it draws lines five times faster than QuickDraw. (Before Tiger, Quartz was slower than QuickDraw, the old Macintosh graphics API that came over as part of Carbon.)  

When Apple finally enables hardware acceleration ("Quartz 2D Extreme"), prepare to have your socks blown off, assuming you have a compatible video card. Hardware-accelerated drawing is eight times faster than the already-accelerated Tiiger software-only drawing mode, and text is three times faster.  

Quartz 2D Extreme has some bugs, so they haven't enabled it in shipping versions of Tiger yet. If you want to play with it, you can use the Quartz Debug app that comes with the developer tools to turn it on temporarily, or issue "sudo defaults write /Library/Preferences/com.apple.windowserver Quartz2DExtremeEnabled -boolean YES" in the terminal to turn it on permanently.  

Drawing stuff faster makes a big difference in how fast the computer feels. Aqua (the Mac OS X UI) looked like liquid before. Now it feels liquid.

I'm certainly impressed with Tiger, and I'll probably buy a mini soon, though I'll still dual boot it with Linux. The truth is, when it comes to frames of mind, Linux is what dropped the scales from my eyes. Using Mac or Windows, I just felt like I was part of the consuming culture. With Mac, a more sophisticated culture, but still, just a consumer.  

But with Linux, I feel like I'm part of a community. Though you need not approach Linux as anything more than a consumer, you can become a part of the Linux community. Open source, by its nature and for better or worse, is only successful to the extent that it's successful in building communities. This is true for development projects, from the kernel down to an audio player, as well as for Linux distributions themselves.  

Not long ago, I decided I wanted to learn my first programming language, and chose Python. Two weeks later, I had written a program that converts audio formats for all the tracks in the amaroK playlist. It's been posted for three weeks, and I've had nearly a thousand downloads. I would never have done this on Win or Mac, partly because programming it would be significantly harder, and partly because it wouldn't be needed. Still, it makes me happy to know that I've improved the lives of a thousand people and counting. I'll stick with the computer that makes me happy, as should everyone.

My impression so far is that 10.4 speeds up all the old functions significantly. The catch, though, is that Spotlight's indexing is now running in the background according to its own idea of when that's appropriate, where obviously there was no such thing in the past. It's an excellent tradeoff, given the return on indexing, but it's still a tradeoff. I'd say that overall, 10.4 feels subjectively a little faster than 10.3.9 in terms of the computer doing things, but quite a bit faster in terms of me accomplishing things.

The big question: is 10.4 continue the trend its predecessors set in being faster than the previous release?  

My puny iBook 800 wants to know. (Aside: I've not upgraded yet, and may not; I'd rather put that money into a new Powerbook someday, and 10.4 will come with it. Knowing my money situation, I'll get that Powerbook about the time that 10.7 comes out.)

My next computer will almost definitely be a Mac Mini, but I doubt if I'll ever understand that kind of proselytizing urge. And I've used Macs at work and via my girlfriend's laptop enough to be pretty certain no scales are going to fall from my eyes when I convert.  

Also, while I accept that working with a given tool (e.g. an operating system) will affect your frame of mind, I don't think a platform is equivalent to one. Maybe the latter explains the former, or vice versa?

And I'm having another recurrence of switcher euphoria after upgrading to Tiger, too. Spotlight actually works! Native arbitrary metadata in the operating system! Even more cross-application integration, even more behind-the-scenes automation, even more toys. Everything even better than it used to be.

Oh, and thank the heavens for glenn (switch)-ing to the Mac and explaining so eloquently why it is a preferable platform/frame-of-mind to Windows, etc. If only everyone would read, and listen, and change...