My first current Mac hasn't arrived yet, so my experience upgrading is with PCs but I expect it to carry over to Macs.
I bought an HP Pavilion with a 500MHz Celeron, 64MB RAM, and 10GB hard drive back in 2000. By mid-2003 it had been upgraded to a 40GB hard drive, 192MB RAM, new case, CD-RW drive, DVD-ROM drive, and GeForce2 MX400 graphics card. Then I got a new motherboard, AMD Athlon XP 2500+ CPU, 512MB RAM, 80GB hard drive, and ATI Radeon 9100 graphics card. So it took 3 years for me to revamp that machine and it needed it by that point since it was a low-end machine when I first bought it. I have since upgraded to an ATI All-in-Wonder 9800 Pro, added a 160GB hard drive, and swapped the CD-RW for a DVD burner. A RAM upgrade and additional hard disk space are the only compelling upgrades I can see for now. I see no reason to upgrade the CPU and motherboard any day soon and expect to get another couple years out of this configuration.
My iBook will have a G4 1.2GHz CPU, 512MB RAM, 60GB hard drive, and a combo drive. I do plan to eventually max the RAM in it and maybe in a few years upgrade the hard drive, but I see no reason why it shouldn't be a good portable computer for the 4-years I am hoping to make it last for. For what I am planning to use it for a 1.2GHz G4 should be more than sufficient, like my desktop the main planned upgrades are just RAM and hard disk space. Since it won't be my primary computer not very much demand will be placed on it.
I bought an HP Pavilion with a 500MHz Celeron, 64MB RAM, and 10GB hard drive back in 2000. By mid-2003 it had been upgraded to a 40GB hard drive, 192MB RAM, new case, CD-RW drive, DVD-ROM drive, and GeForce2 MX400 graphics card. Then I got a new motherboard, AMD Athlon XP 2500+ CPU, 512MB RAM, 80GB hard drive, and ATI Radeon 9100 graphics card. So it took 3 years for me to revamp that machine and it needed it by that point since it was a low-end machine when I first bought it. I have since upgraded to an ATI All-in-Wonder 9800 Pro, added a 160GB hard drive, and swapped the CD-RW for a DVD burner. A RAM upgrade and additional hard disk space are the only compelling upgrades I can see for now. I see no reason to upgrade the CPU and motherboard any day soon and expect to get another couple years out of this configuration.
My iBook will have a G4 1.2GHz CPU, 512MB RAM, 60GB hard drive, and a combo drive. I do plan to eventually max the RAM in it and maybe in a few years upgrade the hard drive, but I see no reason why it shouldn't be a good portable computer for the 4-years I am hoping to make it last for. For what I am planning to use it for a 1.2GHz G4 should be more than sufficient, like my desktop the main planned upgrades are just RAM and hard disk space. Since it won't be my primary computer not very much demand will be placed on it.