I purchased and have installed Mac OS X Tiger 10.4 on my G3 iBook this week. I have to say that Tiger has its ups and its downs. It's not as rosy as you may read elsewhere -- though mostly this is down to me using older hardware.
My first stop was DVD Player. This has received a massive upgrade in Tiger (plus there has since been a Software Update). But many of the new features are not available on older machines. Apple neglects to mention this on the box or in the feature list, but DVD Video Zoom and DVD Video Color are 'Unsupported' on my ATI Mobility Radeon 7500 chip. These are features my PC has had since the Pentium III days, and I feel shafted by this one.
Next stop was Quartz Composer. I am very impressed with this tool, so much so I want to post about it separately. This is going to be a very empowering tool for developers. It's got a bit of Flash in it and more, plus real-time rendering while you develop. This is going places. Even the PC can get in on the action as it can export QuickTime movies. I've yet to explore all of this application (like its patches for interactivity!) but it's more than just a tool for screen savers.
Look out for my post about making an Analog Clock screen saver in Quartz Composer in one hour on the bus.
Today I got around to one of my reasons for Tiger - the new iChat and its much talked about Jabber support. Finally a competent messenger that I have an account for (challenge extended to Microsoft to prove me wrong...). However I took this a step further - I've installed a Jabber server on my laptop and have it working so I don't have to rely on an external Jabber server - only MSN.
Can't say Dashboard has me excited, and I've noticed some glitches in Expose that I don't think were there before (sheets on windows don't highlight, new windows pop up above the Expose layer), but overall if you can't afford to upgrade your Mac (this is the preferred way to get Tiger) it may still be worth the purchase, but you won't get everything.