I personally would prefer Tinker Tool System over Cocktail. While the latter is definitely a good application Tinker Tool System is written by the author of the freeware, Tinker Tool, probably the first utility EVER for MacOSX giving me a bit more confidence, a confidence I've never regretted. There are helpful hints, tips, and definitions in each window for the various optional tasks.
The major item I'd consider necessary would be Alsoft's DiskWarrior and (a poor 2nd choice) Apple's Disk Utility). Presumably the new version of Disk Utility will allow it to check for permissions problems and there is NO utility better at fixing problems, typically based on directory issues, than DiskWarrior.
I'd run it first, followed by a permissions check of the present data. I'd then back all up with an adequate backup application (I use Retrospect 6 and FireWire external drives and have done complete restores with it) or something like CCC as a hedge. CCC is reportedly broken by Tiger so this might want to be an option to carefully consider. Using the "duplicate" function of Retrospect 6 would allow Finder copying of files from /Applications and the two Library files as it simply creates a duplicate of each individual file.
The use of Retrospect 6, or anyother utility that can create a duplicate (using Finder copy is not as accurate as Retrospect IMO because Retrospect has more error checking). Actually any version of Retrospect which works with the present installed OS will work; Just remember to "duplicate" instead of a "backiup" selection for any media.
Then you can do a clean "wipe" (format, including partitioning, if desired before installing Tiger). I don't plan to partition my main drives in PowerBooks or G5s simply because I have a number of backup FireWire drives and a lot of capacity. I'd also backup with Retrospect (or something else if only Finder copy) of /Applications and BOTH Libraries. Many copy protection files live in Preferences and the two libraries, saving a bit of time in entering passwords (you DO have a copy of all passwords, right?). I wouldn't count on Retrospect or ANY other backup application to work under Tiger unless you make a "duplicate" or comparable backup. Obviously you don't want to backup /System unless you know what certain .kext files are that are needed as drivers for (whatever). Hopefully not too many of these will be broken (he said with a wish and a prayer).
I plan to install Tiger on only one of my Macs for the time being and work out the wrinkles with it (I bought a Family Pack). If you have two or more Macs I'd recommend you consider the same thing. That doesn't mean that what works on your G5 will necessarily work on your PowerBook G4, but it should point out some of the many incompatibilities which are inevitable with drivers, not to mention those with assorted applications and utilities which haven't had Tiger upgrades (and need them) yet.