I have used GC for years. Way back to version 2.0.
I've been using version 4.6 now for 4 years and have loved it.
I don't know why I have not upgraded it, but I guess it has served all my needs.
If you ever need a graphics package that does a lot for a small price, this is it.
I'm thinking of upgrading to the newest version soon. Just need to get the wife to let me spend the money.
I have several Macs going back to the original to my two newest Macs.
For the desk top, I'm currently using a PowerMac G4 dual 1.0 GHz shinny door.
For laptop, I just upgraded from an iBook G3 500 15'', to an iBook G4 1.33. 15''.
I have had no problems using GC on any Mac in the past that I can remember.
GC has never failed me. I do use some other software (such as iPhoto) for special needs, but for most everything else, GC is the one I use when it comes to photo manipulation.