Target disk mode is indispensable. I have an x86 linux system with the 2.4 kernel with full firewire support, so imaging was plugging the iBook in and doing "dd if=/dev/sda of=/dev/tape".
I have a VXA tape drive, and for speed, "dd if=/dev/sda bs=1024k | dd of=/dev/tape bs=4096k" seems faster for my specific system, so you can optimize the backup with buffer sizing. I also have Mac partition support, so I probably could do a few more things.
Retrospect under OS 9.1 will NOT PROPERLY BACK UP OS X PARTITIONS. It actually backs up all the files, but it has no knowledge of symlinks, so they end up as small text files with the path where they are supposed to point to upon a restore. This is with HFS+, it can't even see UFS. So I use the target disk mode trick to back up everything else too including my linuxPPC partition.
I Tri-boot, using the option key during startup a lot. Actually I also netboot (Running linuxppc or macos from the above x86 linux box), both my iBook and iMac.
I have a number of data partitions. I copy the system folder and a few other critical things as an alternate boot since it is easy to fix things if you can boot, but if the boot is broken it is much more difficult to fix, so I have my normal Mac OS 9.1 partition and Linux boot partition, and they are mirrored on other data partitions.
The more memory the better. And since ram has become cheap, it is probably the lowest cost performance option. 128k is minimum, 256k is the minimum if you really want to use OS X to its fullest with Classic (that eats 64k) and have all the apps open and switch between them. But I even bought a 512k stick so my iMac DV has 640M.
Partition numbers can get changed by the install so I had to edit my yaboot.conf to boot linux. It took a couple attempts to find hd10 moved to hd12.
Mac doesn't care about partition sequence, but yaboot/linux does (strange things happen when / isn't where /etc/fstab says it is).
Let me second OmniWeb. That is all I use to surf now (the rare exceptions are Netscape under Linux or MacOS 9.1 when I'm booted in those and have to get something).
Another downside is that the ONLY video media OS X currently handles is DV. So my Dazzle Hollywood+ converter works with an NTSC camera, but my old USB webcams don't and won't until a driver is written. I think the Firewire webcams work.
There is a further problem with QuickTime - if you bought the key recently, it will work. But if you upgrade 9.1 to Quicktime 5, it will disable or delete Quicktime 4. So you may want to leave 9.1 at QT 4 if you don't want to upgrade OS X.
Also, there is no "network browser". You have to use the "connect to server" which is like the chooser. It works but I find it less convenient.
And you will eventually need to learn how to use NetInfo Manager (in Applications/Utilities). This sets the kinds of things which are normally in /etc/hosts, /etc/passwd, and /etc/resolv.conf (but are overridden by lookupd - think of how NIS works). Much of this can be configured by the various System Preferences and other apps, but they do so by making netinfo entries.