Apple has been busy in the last few weeks with updates to QuickTime, iTunes, Safari, and their old Security Update. Problems were obvious with some right away, but others took a while to discover.
Many of you did update when Software Update popped up and told you to, and things have worked correctly. You may breathe a sigh of relief.
The worst offender is the 2008-004 Security Update for Tiger (10.4). This has a bug that causes your Network pane in System Preferences to drop a dialog box that says "Your settings have been changed by another application." with an OK button. Click it and immediately it pops up again. This affects everyone running OSX 10.4.11, whether on an Intel Mac or a PPC Mac.
Fortunately, if you don't need to change your settings in this panel, your Internet connection will continue to work. You will even be able to switch between plug-in Ethernet cabling and wireless AirPort, and move your connection between other WiFi spots (your neighbor, a coffee house, work, etc.)
There is no fix. After going round and round with Apple on this recently, and being kicked upstairs to one of the people who really know what's going on, the bottom line is you have to do an Archive and Install reinstallation from your Tiger disk, and then run all the Software Updates again, EXCEPT for the offending Security Update.
Or just give up and buy Leopard 10.5, assuming your Mac has enough RAM and is fast enough to use it.
Safari - The last stable version is 3.1.2. There have been two updates, 3.2 and 3.2.1 since. Besides disabling add-on programs like PithHelmet (which blocks ads) and other input managers, the update is much more sensitive to misbehaving sites and crashes quite often. One workaround, if you have already gotten the update, is to go to the Safari menu and choose Empty Cache, then again and choose Reset Safari. Let it delete your entire history, saved passwords, icons, etc. This has been shown to help make it more stable. But if you are running 3.1.2 or older, stop there. This affects people running OSX 10.4.11 and also 10.5.5.
Leopard - I have had no trouble with the 10.5.5 update, compared to the stable 10.5.4 version that is on the store-bought DVDs currently available. (Previous store copies were 10.5.1, which replaced the notoriously buggy initial 10.5 release.) The notorious exception affects people using ProTools, the music composition suite of software. They have experienced display issues when updating to 10.5.5 and the only fix is to reinstall and then stop at 10.5.4.
QuickTime - The problematic version is 7.5.5. The previous 7.5 is pretty stable but if you have 7.3 or 7.4.5, don't update unless getting a new iPhone forces you to. Users are experiencing playback problems with the newest version on some web pages.
iTunes 8 - The latest is 8.0.2 but any version past 7.7 has introduced difficulties for some. The biggest problems have been experienced by people who store their iTunes library on a different hard drive from the startup drive. It loses track of the library data and usually requires recreating the library, which causes you to lose all of your playlists. Outside of a cool visualizer eye-candy effect, and a "genius sidebar" that takes note of what you are playing and suggests other songs you can buy from the iTunes Store, there is no advantage to iTunes 8. It's required, of course, if you have the latest iPhone.
The new MacBooks - The Defective By Design web site, an informational service opposed to DRM (Digital Rights Management, or copy protection), has listed the new MacBooks as #1 in their 35 Days Against DRM project. Read all about it at Defective By Design. It seems Apple has included a hardware chip in the new models that serves no function other than to make it impossible to play certain video formats that are deemed "the analog hole," or a format the movie and TV industry has decided you may not view.
I realize this affects very few of you, but if you want to rip video from your TV, or from a DVD, you have to go through extra hoops to make it work. It is a consumer-hostile act on Apple's part, and they should not be allowed to get away without hearing protest from their customers. This chip has not been included in any of their other models - yet.