If you have some knowledge of unix and linux systems, having a powerpc mac with something like 10.5.8 or 10.4.11 isn't just a fun project, but it should be treated as a matter of security.
Bash, as well as other shells, can be installed / updated and security patches can be added from macports. Because most modern computers are intel-type CPU's (AMD, Intel) viruses are also rather rare if not non-existent. While gaming and internet use is limited away from flash items like youtube, most tools from unix/linux have ppc ports, such as KDenLive (a video editor and my personal choice), and the use made of the powerpc processor is made rather well. Video editing can also be easily done with just an old version of final cut or a new version of avidemux (if you know how to use it).
Also as a note using mactubes or youview for youtube effectively removes any flash scare, however somewhere there is a webpage containing flash 11.5. I have the file as well ,so I may upload it at some point. The only reason to have the plugin is to plug the security hole in the OS that is there.
Any other issues as such should be researched thoroughly. I am currently working on making minecraft 1.8 work. My first issue is java 1.6 I have the files for it and supposedly it will work fine (openJDK ported to PPC OSX) but I honestly have no idea where to put what and how to do any of what needs ot be done. Though by christmas I should have the latest minecraft! Excitement! I will post how to do it once I figure that out.