In TidBITS-318 Geoff reported on System 7.5.3, and in TidBITS-322 and TidBITS-323, I talked about how you might obtain the update. Reports I've seen suggest once you've successfully installed 7.5.3 you won't encounter many compatibility problems. Even so, users of Connectix's RAM Doubler and Speed Doubler, as well as Symantec's AntiVirus for Macintosh may save themselves a great deal of hair-pulling by checking out the rest of this article.
Speed Doubler -- Speed Doubler users running 7.5.3 must update to version 1.1.2, which is available via Connectix's Web site. If you need a localized version, note that Connectix should start posting localized versions later this week.
RAM Doubler -- If you run RAM Doubler on a 68K-based PowerBook (but not any PowerBook using a PowerPC chip) the machine is likely to experience Type 8 errors upon awakening from sleep. To avoid this particular problem, either disable RAM Doubler or try installing MacsBug 6.5.3, which - according to Connectix - blocks the problem.
In case you were wondering, MacsBug is a low-level programming debugger. It won't fix bugs, but programmers use it to isolate bugs and there's no harm in non-programmers using it. To install MacsBug, place it in your System Folder and restart. After that, other than a "Debugger Installed" message in the Welcome to Macintosh startup screen, you shouldn't be able to tell that MacsBug is installed - it doesn't have a control panel, put icons in your menubar, or anything like that. However, if you crash, you may be "dumped" into MacsBug, a black and white display with lots of numbers and low-level programming stuff. To recover from the crash, try these techniques, in this order:
Type g and press return. (G stands for Go.) In a few instances, this may return you to what you were doing.
If g doesn't work, type es. (ES stands for Exit to Shell - it's like Command-Option-Escape in System 7.x.) This might return you to the Finder. If it does, quickly save any unsaved work in other applications and restart normally.
If es doesn't work, type rs. (RS stands for Restart.) This should restart the computer, though you won't get to save any unsaved work.
If rs doesn't work, do whatever you normally do when your Mac freezes (you might press a reset button or Command-Control-Power).
Getting back on topic, if you have RAM Doubler with System 7.5.3 on a 68040-based Macintosh (but not the 660AV or 840AV) you are likely to crash while copying files in the Finder. MacsBug won't help with this problem, though Connectix plans to fix all these problems in the next release of RAM Doubler.
SAM -- If you update to 7.5.3, run SAM, and receive an error message saying SAM can't find its Virus Definitions file, you can solve the problem by updating to SAM 4.0.8. (Symantec recommends 4.0.8 for anyone running 7.5.2 or 7.5.3). A patcher is available at Symantec's FTP site.
If the 7.5.3 Update has become an important part of your life, and you want to stay abreast of each and every incompatibility, you might monitor Julian Daniel's 7.5.3 Tips site as well as Macworld News's running list of 7.5.3 incompatibilities, by Roxanne Gentile.